diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
index cd9e1c8..791daa6 100644
--- a/LayoutTests/ChangeLog
+++ b/LayoutTests/ChangeLog
@@ -1,3 +1,16 @@
+2019-10-16  John Wilander  <wilander@apple.com>
+
+        Resource Load Statistics (experimental): Block all third-party cookies on websites without prior user interaction
+        https://bugs.webkit.org/show_bug.cgi?id=203017
+        <rdar://problem/56262708>
+
+        Reviewed by Alex Christensen.
+
+        * http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database-expected.txt: Added.
+        * http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database.html: Added.
+        * http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-expected.txt: Added.
+        * http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html: Added.
+
 2019-10-16  Russell Epstein  <repstein@apple.com>
 
         Correct TestExpectations from r251119.
diff --git a/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database-expected.txt b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database-expected.txt
new file mode 100644
index 0000000..a7fed3a
--- /dev/null
+++ b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database-expected.txt
@@ -0,0 +1,25 @@
+Tests that all third-party cookies are blocked under websites that have not received user interaction.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+  
+
+--------
+Frame: '<!--frame1-->'
+--------
+Before user interaction, should receive no cookies.
+Did not receive cookie named 'firstPartyCookie'.
+Did not receive cookie named 'partitionedCookie'.
+Client-side document.cookie:
+
+--------
+Frame: '<!--frame2-->'
+--------
+After user interaction, should receive first-party cookie.
+Received cookie named 'firstPartyCookie'.
+Did not receive cookie named 'partitionedCookie'.
+Client-side document.cookie: firstPartyCookie=value
diff --git a/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database.html b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database.html
new file mode 100644
index 0000000..fc9233c
--- /dev/null
+++ b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database.html
@@ -0,0 +1,78 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <script src="/js-test-resources/js-test.js"></script>
+    <script src="resources/util.js"></script>
+</head>
+<body>
+<script>
+    description("Tests that all third-party cookies are blocked under websites that have not received user interaction.");
+    jsTestIsAsync = true;
+
+    const partitionHost = "127.0.0.1:8000";
+    const partitionOrigin = "http://" + partitionHost;
+    const thirdPartyOrigin = "http://localhost:8000";
+    const resourcePath = "/resourceLoadStatistics/resources";
+    const thirdPartyBaseUrl = thirdPartyOrigin + resourcePath;
+    const firstPartyCookieName = "firstPartyCookie";
+    const subPathToSetFirstPartyCookie = "/set-cookie.php?name=" + firstPartyCookieName + "&value=value";
+    const partitionedCookieName = "partitionedCookie";
+    const subPathToSetPartitionedCookie = "/set-cookie.php?name=" + partitionedCookieName + "&value=value";
+    const returnUrl = partitionOrigin + "/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html";
+    const subPathToGetCookies = "/get-cookies.php?name1=" + firstPartyCookieName + "&name2=" + partitionedCookieName;
+
+    function openIframe(url, onLoadHandler) {
+        const element = document.createElement("iframe");
+        element.src = url;
+        if (onLoadHandler) {
+            element.onload = onLoadHandler;
+        }
+        document.body.appendChild(element);
+    }
+
+    function runTest() {
+        switch (document.location.hash) {
+            case "#step1":
+                // Set first-party cookie for localhost.
+                document.location.href = thirdPartyBaseUrl + subPathToSetFirstPartyCookie + "#" + returnUrl + "#step2";
+                break;
+            case "#step2":
+                document.location.hash = "step3";
+                // Check that the cookie is blocked for localhost under 127.0.0.1 even though localhost is not prevalent.
+                openIframe(thirdPartyBaseUrl + subPathToGetCookies + "&message=Before user interaction, should receive no cookies.", runTest);
+                break;
+            case "#step3":
+                document.location.hash = "step4";
+                // Produce user interaction for the first-party to allow third-party cookie access.
+                testRunner.setStatisticsHasHadUserInteraction(partitionOrigin, true, function() {
+                    testRunner.statisticsUpdateCookieBlocking(function() {
+                        // Check that the cookie is no longer blocked for localhost under 127.0.0.1.
+                        openIframe(thirdPartyBaseUrl + subPathToGetCookies +  "&message=After user interaction, should receive first-party cookie.", runTest);
+                    });
+                });
+                break;
+            case "#step4":
+                testRunner.setUseITPDatabase(false);
+                testRunner.setStatisticsShouldBlockThirdPartyCookies(false, function() {
+                    setEnableFeature(false, finishJSTest);
+                });
+                break;
+        }
+    }
+
+    if (document.location.hash === "") {
+        testRunner.setUseITPDatabase(true);
+        setEnableFeature(true, function () {
+            if (testRunner.isStatisticsPrevalentResource(thirdPartyOrigin))
+                testFailed("Localhost was classified as prevalent resource before the test starts.");
+            testRunner.dumpChildFramesAsText();
+            document.location.hash = "step1";
+            testRunner.setStatisticsShouldBlockThirdPartyCookies(true, runTest);
+        });
+    } else {
+        runTest();
+    }
+</script>
+</body>
+</html>
diff --git a/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-expected.txt b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-expected.txt
new file mode 100644
index 0000000..a7fed3a
--- /dev/null
+++ b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-expected.txt
@@ -0,0 +1,25 @@
+Tests that all third-party cookies are blocked under websites that have not received user interaction.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+  
+
+--------
+Frame: '<!--frame1-->'
+--------
+Before user interaction, should receive no cookies.
+Did not receive cookie named 'firstPartyCookie'.
+Did not receive cookie named 'partitionedCookie'.
+Client-side document.cookie:
+
+--------
+Frame: '<!--frame2-->'
+--------
+After user interaction, should receive first-party cookie.
+Received cookie named 'firstPartyCookie'.
+Did not receive cookie named 'partitionedCookie'.
+Client-side document.cookie: firstPartyCookie=value
diff --git a/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html
new file mode 100644
index 0000000..cdf7323
--- /dev/null
+++ b/LayoutTests/http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html
@@ -0,0 +1,76 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <script src="/js-test-resources/js-test.js"></script>
+    <script src="resources/util.js"></script>
+</head>
+<body>
+<script>
+    description("Tests that all third-party cookies are blocked under websites that have not received user interaction.");
+    jsTestIsAsync = true;
+
+    const partitionHost = "127.0.0.1:8000";
+    const partitionOrigin = "http://" + partitionHost;
+    const thirdPartyOrigin = "http://localhost:8000";
+    const resourcePath = "/resourceLoadStatistics/resources";
+    const thirdPartyBaseUrl = thirdPartyOrigin + resourcePath;
+    const firstPartyCookieName = "firstPartyCookie";
+    const subPathToSetFirstPartyCookie = "/set-cookie.php?name=" + firstPartyCookieName + "&value=value";
+    const partitionedCookieName = "partitionedCookie";
+    const subPathToSetPartitionedCookie = "/set-cookie.php?name=" + partitionedCookieName + "&value=value";
+    const returnUrl = partitionOrigin + "/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html";
+    const subPathToGetCookies = "/get-cookies.php?name1=" + firstPartyCookieName + "&name2=" + partitionedCookieName;
+
+    function openIframe(url, onLoadHandler) {
+        const element = document.createElement("iframe");
+        element.src = url;
+        if (onLoadHandler) {
+            element.onload = onLoadHandler;
+        }
+        document.body.appendChild(element);
+    }
+
+    function runTest() {
+        switch (document.location.hash) {
+            case "#step1":
+                // Set first-party cookie for localhost.
+                document.location.href = thirdPartyBaseUrl + subPathToSetFirstPartyCookie + "#" + returnUrl + "#step2";
+                break;
+            case "#step2":
+                document.location.hash = "step3";
+                // Check that the cookie is blocked for localhost under 127.0.0.1 even though localhost is not prevalent.
+                openIframe(thirdPartyBaseUrl + subPathToGetCookies + "&message=Before user interaction, should receive no cookies.", runTest);
+                break;
+            case "#step3":
+                document.location.hash = "step4";
+                // Produce user interaction for the first-party to allow third-party cookie access.
+                testRunner.setStatisticsHasHadUserInteraction(partitionOrigin, true, function() {
+                    testRunner.statisticsUpdateCookieBlocking(function() {
+                        // Check that the cookie is no longer blocked for localhost under 127.0.0.1.
+                        openIframe(thirdPartyBaseUrl + subPathToGetCookies +  "&message=After user interaction, should receive first-party cookie.", runTest);
+                    });
+                });
+                break;
+            case "#step4":
+                testRunner.setStatisticsShouldBlockThirdPartyCookies(false, function() {
+                    setEnableFeature(false, finishJSTest);
+                });
+                break;
+        }
+    }
+
+    if (document.location.hash === "") {
+        setEnableFeature(true, function () {
+            if (testRunner.isStatisticsPrevalentResource(thirdPartyOrigin))
+                testFailed("Localhost was classified as prevalent resource before the test starts.");
+            testRunner.dumpChildFramesAsText();
+            document.location.hash = "step1";
+            testRunner.setStatisticsShouldBlockThirdPartyCookies(true, runTest);
+        });
+    } else {
+        runTest();
+    }
+</script>
+</body>
+</html>
diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 2f24c2a..5dfd194 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,31 @@
+2019-10-16  John Wilander  <wilander@apple.com>
+
+        Resource Load Statistics (experimental): Block all third-party cookies on websites without prior user interaction
+        https://bugs.webkit.org/show_bug.cgi?id=203017
+        <rdar://problem/56262708>
+
+        Reviewed by Alex Christensen.
+
+        NetworkStorageSession::shouldBlockCookies() now checks if the first-party website has
+        received user interaction and if not, blocks all third-party cookies, regardless of the
+        status of those third-party domains (prevalent or not).
+
+        Bundled cleanup task: Remove the two month old feature flag for NSURLSession switching.
+
+        Tests: http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction-database.html
+               http/tests/resourceLoadStatistics/third-party-cookie-blocking-on-sites-without-user-interaction.html
+
+        * page/RuntimeEnabledFeatures.h:
+        (WebCore::RuntimeEnabledFeatures::setIsITPSessionSwitchingEnabled): Deleted.
+        (WebCore::RuntimeEnabledFeatures::isITPSessionSwitchingEnabled const): Deleted.
+        * page/Settings.yaml:
+        * platform/network/NetworkStorageSession.cpp:
+        (WebCore::NetworkStorageSession::hasHadUserInteractionAsFirstParty const):
+        (WebCore::NetworkStorageSession::shouldBlockCookies const):
+        (WebCore::NetworkStorageSession::setDomainsWithUserInteractionAsFirstParty):
+        * platform/network/NetworkStorageSession.h:
+        (WebCore::NetworkStorageSession::setIsThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled):
+
 2019-10-16  Zalan Bujtas  <zalan@apple.com>
 
         [LFC][IFC] Add style and text content to Display::Run
diff --git a/Source/WebCore/page/RuntimeEnabledFeatures.h b/Source/WebCore/page/RuntimeEnabledFeatures.h
index 3bbbb14..3d4c56b 100644
--- a/Source/WebCore/page/RuntimeEnabledFeatures.h
+++ b/Source/WebCore/page/RuntimeEnabledFeatures.h
@@ -147,9 +147,6 @@
     void setIsITPDatabaseEnabled(bool isEnabled) { m_isITPDatabaseEnabled = isEnabled; }
     bool isITPDatabaseEnabled() const { return m_isITPDatabaseEnabled; }
 
-    void setIsITPSessionSwitchingEnabled(bool isEnabled) { m_isITPSessionSwitchingEnabled = isEnabled; }
-    bool isITPSessionSwitchingEnabled() const { return m_isITPSessionSwitchingEnabled; }
-
     void setRestrictedHTTPResponseAccess(bool isEnabled) { m_isRestrictedHTTPResponseAccess = isEnabled; }
     bool restrictedHTTPResponseAccess() const { return m_isRestrictedHTTPResponseAccess; }
 
@@ -420,7 +417,6 @@
     bool m_accessibilityObjectModelEnabled { false };
     bool m_ariaReflectionEnabled { true };
     bool m_itpDebugMode { false };
-    bool m_isITPSessionSwitchingEnabled { true };
     bool m_isRestrictedHTTPResponseAccess { true };
     bool m_crossOriginResourcePolicyEnabled { true };
     bool m_isWebGLCompressedTextureASTCSupportEnabled { false };
diff --git a/Source/WebCore/page/Settings.yaml b/Source/WebCore/page/Settings.yaml
index 47f0ed6..88c3789 100644
--- a/Source/WebCore/page/Settings.yaml
+++ b/Source/WebCore/page/Settings.yaml
@@ -869,8 +869,8 @@
   initial: true
   inspectorOverride: true
 
-isITPSessionSwitchingEnabled:
-  initial: true
+isThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled:
+  initial: false
 
 isLoggedInAPIEnabled:
   initial: false
diff --git a/Source/WebCore/platform/network/NetworkStorageSession.cpp b/Source/WebCore/platform/network/NetworkStorageSession.cpp
index 31d575f..2c4556a 100644
--- a/Source/WebCore/platform/network/NetworkStorageSession.cpp
+++ b/Source/WebCore/platform/network/NetworkStorageSession.cpp
@@ -78,6 +78,14 @@
     return m_registrableDomainsToBlockButKeepCookiesFor.contains(registrableDomain);
 }
 
+bool NetworkStorageSession::hasHadUserInteractionAsFirstParty(const RegistrableDomain& registrableDomain) const
+{
+    if (registrableDomain.isEmpty())
+        return false;
+
+    return m_registrableDomainsWithUserInteractionAsFirstParty.contains(registrableDomain);
+}
+
 bool NetworkStorageSession::shouldBlockCookies(const ResourceRequest& request, Optional<FrameIdentifier> frameID, Optional<PageIdentifier> pageID) const
 {
     return shouldBlockCookies(request.firstPartyForCookies(), request.url(), frameID, pageID);
@@ -99,6 +107,9 @@
     if (pageID && hasStorageAccess(resourceDomain, firstPartyDomain, frameID, pageID.value()))
         return false;
 
+    if (m_isThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled && !hasHadUserInteractionAsFirstParty(firstPartyDomain))
+        return true;
+
     return shouldBlockThirdPartyCookies(resourceDomain);
 }
 
@@ -127,6 +138,12 @@
     m_registrableDomainsToBlockButKeepCookiesFor.add(domains.begin(), domains.end());
 }
 
+void NetworkStorageSession::setDomainsWithUserInteractionAsFirstParty(const Vector<RegistrableDomain>& domains)
+{
+    m_registrableDomainsWithUserInteractionAsFirstParty.clear();
+    m_registrableDomainsWithUserInteractionAsFirstParty.add(domains.begin(), domains.end());
+}
+
 void NetworkStorageSession::removePrevalentDomains(const Vector<RegistrableDomain>& domains)
 {
     for (auto& domain : domains) {
diff --git a/Source/WebCore/platform/network/NetworkStorageSession.h b/Source/WebCore/platform/network/NetworkStorageSession.h
index 5bb8437..2038b88 100644
--- a/Source/WebCore/platform/network/NetworkStorageSession.h
+++ b/Source/WebCore/platform/network/NetworkStorageSession.h
@@ -147,8 +147,10 @@
     WEBCORE_EXPORT bool shouldBlockCookies(const URL& firstPartyForCookies, const URL& resource, Optional<FrameIdentifier>, Optional<PageIdentifier>) const;
     WEBCORE_EXPORT bool shouldBlockThirdPartyCookies(const RegistrableDomain&) const;
     WEBCORE_EXPORT bool shouldBlockThirdPartyCookiesButKeepFirstPartyCookiesFor(const RegistrableDomain&) const;
+    WEBCORE_EXPORT bool hasHadUserInteractionAsFirstParty(const RegistrableDomain&) const;
     WEBCORE_EXPORT void setPrevalentDomainsToBlockAndDeleteCookiesFor(const Vector<RegistrableDomain>&);
     WEBCORE_EXPORT void setPrevalentDomainsToBlockButKeepCookiesFor(const Vector<RegistrableDomain>&);
+    WEBCORE_EXPORT void setDomainsWithUserInteractionAsFirstParty(const Vector<RegistrableDomain>&);
     WEBCORE_EXPORT void setAgeCapForClientSideCookies(Optional<Seconds>);
     WEBCORE_EXPORT void removePrevalentDomains(const Vector<RegistrableDomain>& domains);
     WEBCORE_EXPORT bool hasStorageAccess(const RegistrableDomain& resourceDomain, const RegistrableDomain& firstPartyDomain, Optional<FrameIdentifier>, PageIdentifier) const;
@@ -162,6 +164,7 @@
     WEBCORE_EXPORT Optional<Seconds> maxAgeCacheCap(const ResourceRequest&);
     WEBCORE_EXPORT void didCommitCrossSiteLoadWithDataTransferFromPrevalentResource(const RegistrableDomain& toDomain, PageIdentifier);
     WEBCORE_EXPORT void resetCrossSiteLoadsWithLinkDecorationForTesting();
+    void setIsThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled(bool enabled) { m_isThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled = enabled; }
 #endif
 
 private:
@@ -188,6 +191,7 @@
     Optional<Seconds> clientSideCookieCap(const RegistrableDomain& firstParty, Optional<PageIdentifier>) const;
     HashSet<RegistrableDomain> m_registrableDomainsToBlockAndDeleteCookiesFor;
     HashSet<RegistrableDomain> m_registrableDomainsToBlockButKeepCookiesFor;
+    HashSet<RegistrableDomain> m_registrableDomainsWithUserInteractionAsFirstParty;
     HashMap<PageIdentifier, HashMap<FrameIdentifier, RegistrableDomain>> m_framesGrantedStorageAccess;
     HashMap<PageIdentifier, HashMap<RegistrableDomain, RegistrableDomain>> m_pagesGrantedStorageAccess;
     Optional<Seconds> m_cacheMaxAgeCapForPrevalentResources { };
@@ -195,6 +199,7 @@
     Optional<Seconds> m_ageCapForClientSideCookiesShort { };
     HashMap<WebCore::PageIdentifier, RegistrableDomain> m_navigatedToWithLinkDecorationByPrevalentResource;
     bool m_navigationWithLinkDecorationTestMode = false;
+    bool m_isThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled = false;
 #endif
 
 #if PLATFORM(COCOA)
diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
index a4a3466..3ed827b 100644
--- a/Source/WebKit/ChangeLog
+++ b/Source/WebKit/ChangeLog
@@ -1,3 +1,71 @@
+2019-10-16  John Wilander  <wilander@apple.com>
+
+        Resource Load Statistics (experimental): Block all third-party cookies on websites without prior user interaction
+        https://bugs.webkit.org/show_bug.cgi?id=203017
+        <rdar://problem/56262708>
+
+        Reviewed by Alex Christensen.
+
+        This enhancement is off by default and controlled by an internal feature flag.
+
+        The functional change is in WebCore::NetworkStorageSession::shouldBlockCookies() which is
+        called from:
+        - NetworkDataTaskCocoa::NetworkDataTaskCocoa()
+        - NetworkDataTaskCocoa::willPerformHTTPRedirection
+
+        shouldBlockCookies() now checks if the first-party website has received user interaction
+        and if not, blocks all third-party cookies, regardless of the status of those third-party
+        domains (prevalent or not).
+
+        The changes to ResourceLoadStatisticsDatabaseStore and ResourceLoadStatisticsMemoryStore
+        are about communicating which domains have received user interaction (prevalent or not)
+        to the network storage session so that it can enforce the new restriction.
+
+        The C API change and piping through the WebsiteDataStore is test infrastructure.
+
+        Bundled cleanup task: Remove the two month old feature flag for NSURLSession switching.
+
+        * NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.cpp:
+        (WebKit::CompletionHandler<void):
+        * NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.h:
+        * NetworkProcess/Classifier/ResourceLoadStatisticsMemoryStore.cpp:
+        (WebKit::ResourceLoadStatisticsMemoryStore::clear):
+        (WebKit::ResourceLoadStatisticsMemoryStore::updateCookieBlocking):
+        * NetworkProcess/Classifier/WebResourceLoadStatisticsStore.cpp:
+        (WebKit::WebResourceLoadStatisticsStore::callUpdatePrevalentDomainsToBlockCookiesForHandler):
+        * NetworkProcess/Classifier/WebResourceLoadStatisticsStore.h:
+        (WebKit::RegistrableDomainsToBlockCookiesFor::isolatedCopy const):
+        * NetworkProcess/NetworkProcess.cpp:
+        (WebKit::NetworkProcess::initializeNetworkProcess):
+        (WebKit::NetworkProcess::setShouldBlockThirdPartyCookiesForTesting):
+        * NetworkProcess/NetworkProcess.messages.in:
+        * NetworkProcess/NetworkSession.cpp:
+        (WebKit::NetworkSession::NetworkSession):
+        * NetworkProcess/NetworkSession.h:
+        (WebKit::NetworkSession::setResourceLoadStatisticsLogTestingEvent):
+        (WebKit::NetworkSession::shouldIsolateSessionsForPrevalentTopFrames const): Deleted.
+        * NetworkProcess/NetworkSessionCreationParameters.cpp:
+        (WebKit::NetworkSessionCreationParameters::encode const):
+        (WebKit::NetworkSessionCreationParameters::decode):
+        * NetworkProcess/NetworkSessionCreationParameters.h:
+        * NetworkProcess/cocoa/NetworkDataTaskCocoa.mm:
+        (WebKit::NetworkDataTaskCocoa::NetworkDataTaskCocoa):
+        * NetworkProcess/cocoa/NetworkSessionCocoa.mm:
+        (WebKit::NetworkSessionCocoa::NetworkSessionCocoa):
+        * Shared/WebPreferences.yaml:
+        * UIProcess/API/C/WKWebsiteDataStoreRef.cpp:
+        (WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting):
+        (WKWebsiteDataStoreStatisticsResetToConsistentState):
+        * UIProcess/API/C/WKWebsiteDataStoreRef.h:
+        * UIProcess/Network/NetworkProcessProxy.cpp:
+        (WebKit::NetworkProcessProxy::setShouldBlockThirdPartyCookiesForTesting):
+        * UIProcess/Network/NetworkProcessProxy.h:
+        * UIProcess/WebsiteData/Cocoa/WebsiteDataStoreCocoa.mm:
+        (WebKit::WebsiteDataStore::parameters):
+        * UIProcess/WebsiteData/WebsiteDataStore.cpp:
+        (WebKit::WebsiteDataStore::setResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting):
+        * UIProcess/WebsiteData/WebsiteDataStore.h:
+
 2019-10-16  Kate Cheney  <katherine_cheney@apple.com>
 
         WKWebsiteDataStoreStatisticsResetToConsistentState() should call store.setUseITPDatabase(false)
diff --git a/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.cpp b/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.cpp
index 1db541e..eb94abb 100644
--- a/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.cpp
+++ b/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.cpp
@@ -1680,7 +1680,7 @@
     removeAllStorageAccess([callbackAggregator = callbackAggregator.copyRef()] { });
 
     auto registrableDomainsToBlockAndDeleteCookiesFor = ensurePrevalentResourcesForDebugMode();
-    RegistrableDomainsToBlockCookiesFor domainsToBlock { registrableDomainsToBlockAndDeleteCookiesFor, { } };
+    RegistrableDomainsToBlockCookiesFor domainsToBlock { registrableDomainsToBlockAndDeleteCookiesFor, { }, { } };
     updateCookieBlockingForDomains(domainsToBlock, [callbackAggregator = callbackAggregator.copyRef()] { });
 }
 
@@ -1752,19 +1752,35 @@
     return results;
 }
 
+Vector<RegistrableDomain> ResourceLoadStatisticsDatabaseStore::domainsWithUserInteractionAsFirstParty() const
+{
+    ASSERT(!RunLoop::isMain());
+
+    Vector<RegistrableDomain> results;
+    SQLiteStatement statement(m_database, "SELECT registrableDomain FROM ObservedDomains WHERE hadUserInteraction = 1"_s);
+    if (statement.prepare() != SQLITE_OK)
+        return results;
+    
+    while (statement.step() == SQLITE_ROW)
+        results.append(RegistrableDomain::uncheckedCreateFromRegistrableDomainString(statement.getColumnText(0)));
+
+    return results;
+}
+
 void ResourceLoadStatisticsDatabaseStore::updateCookieBlocking(CompletionHandler<void()>&& completionHandler)
 {
     ASSERT(!RunLoop::isMain());
 
     auto domainsToBlockAndDeleteCookiesFor = this->domainsToBlockAndDeleteCookiesFor();
     auto domainsToBlockButKeepCookiesFor = this->domainsToBlockButKeepCookiesFor();
+    auto domainsWithUserInteractionAsFirstParty = this->domainsWithUserInteractionAsFirstParty();
 
-    if (domainsToBlockAndDeleteCookiesFor.isEmpty() && domainsToBlockButKeepCookiesFor.isEmpty()) {
+    if (domainsToBlockAndDeleteCookiesFor.isEmpty() && domainsToBlockButKeepCookiesFor.isEmpty() && domainsWithUserInteractionAsFirstParty.isEmpty()) {
         completionHandler();
         return;
     }
 
-    RegistrableDomainsToBlockCookiesFor domainsToBlock { domainsToBlockAndDeleteCookiesFor, domainsToBlockButKeepCookiesFor };
+    RegistrableDomainsToBlockCookiesFor domainsToBlock { domainsToBlockAndDeleteCookiesFor, domainsToBlockButKeepCookiesFor, domainsWithUserInteractionAsFirstParty };
 
     if (debugLoggingEnabled() && !domainsToBlockAndDeleteCookiesFor.isEmpty() && !domainsToBlockButKeepCookiesFor.isEmpty())
         debugLogDomainsInBatches("block", domainsToBlock);
diff --git a/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.h b/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.h
index beed834..0226325 100644
--- a/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.h
+++ b/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.h
@@ -155,6 +155,7 @@
     void setUserInteraction(const RegistrableDomain&, bool hadUserInteraction, WallTime);
     Vector<RegistrableDomain> domainsToBlockAndDeleteCookiesFor() const;
     Vector<RegistrableDomain> domainsToBlockButKeepCookiesFor() const;
+    Vector<RegistrableDomain> domainsWithUserInteractionAsFirstParty() const;
 
     struct PrevalentDomainData {
         unsigned domainID;
diff --git a/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsMemoryStore.cpp b/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsMemoryStore.cpp
index 6589f6b..f92f4fd 100644
--- a/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsMemoryStore.cpp
+++ b/Source/WebKit/NetworkProcess/Classifier/ResourceLoadStatisticsMemoryStore.cpp
@@ -697,7 +697,7 @@
     removeAllStorageAccess([callbackAggregator = callbackAggregator.copyRef()] { });
 
     auto registrableDomainsToBlockAndDeleteCookiesFor = ensurePrevalentResourcesForDebugMode();
-    RegistrableDomainsToBlockCookiesFor domainsToBlock { registrableDomainsToBlockAndDeleteCookiesFor, { } };
+    RegistrableDomainsToBlockCookiesFor domainsToBlock { registrableDomainsToBlockAndDeleteCookiesFor, { }, { } };
     updateCookieBlockingForDomains(domainsToBlock, [callbackAggregator = callbackAggregator.copyRef()] { });
 }
 
@@ -735,21 +735,22 @@
 
     Vector<RegistrableDomain> domainsToBlockAndDeleteCookiesFor;
     Vector<RegistrableDomain> domainsToBlockButKeepCookiesFor;
+    Vector<RegistrableDomain> domainsWithUserInteractionAsFirstParty;
     for (auto& resourceStatistic : m_resourceStatisticsMap.values()) {
-        if (resourceStatistic.isPrevalentResource) {
-            if (hasHadUnexpiredRecentUserInteraction(resourceStatistic, OperatingDatesWindow::Long))
-                domainsToBlockButKeepCookiesFor.append(resourceStatistic.registrableDomain);
-            else
-                domainsToBlockAndDeleteCookiesFor.append(resourceStatistic.registrableDomain);
-        }
+        if (hasHadUnexpiredRecentUserInteraction(resourceStatistic, OperatingDatesWindow::Long)) {
+            if (resourceStatistic.isPrevalentResource)
+                domainsToBlockButKeepCookiesFor.append(resourceStatistic.registrableDomain.isolatedCopy());
+            domainsWithUserInteractionAsFirstParty.append(resourceStatistic.registrableDomain);
+        } else if (resourceStatistic.isPrevalentResource)
+            domainsToBlockAndDeleteCookiesFor.append(resourceStatistic.registrableDomain);
     }
 
-    if (domainsToBlockAndDeleteCookiesFor.isEmpty() && domainsToBlockButKeepCookiesFor.isEmpty() && !debugModeEnabled()) {
+    if (domainsToBlockAndDeleteCookiesFor.isEmpty() && domainsToBlockButKeepCookiesFor.isEmpty() && domainsWithUserInteractionAsFirstParty.isEmpty() && !debugModeEnabled()) {
         completionHandler();
         return;
     }
 
-    RegistrableDomainsToBlockCookiesFor domainsToBlock { domainsToBlockAndDeleteCookiesFor, domainsToBlockButKeepCookiesFor };
+    RegistrableDomainsToBlockCookiesFor domainsToBlock { domainsToBlockAndDeleteCookiesFor, domainsToBlockButKeepCookiesFor, domainsWithUserInteractionAsFirstParty };
 
     if (debugLoggingEnabled() && !domainsToBlockAndDeleteCookiesFor.isEmpty() && !domainsToBlockButKeepCookiesFor.isEmpty())
         debugLogDomainsInBatches("block", domainsToBlock);
diff --git a/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.cpp b/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.cpp
index e08ab5d..7b8adec 100644
--- a/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.cpp
+++ b/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.cpp
@@ -965,6 +965,7 @@
         if (auto* storageSession = m_networkSession->networkStorageSession()) {
             storageSession->setPrevalentDomainsToBlockAndDeleteCookiesFor(domainsToBlock.domainsToBlockAndDeleteCookiesFor);
             storageSession->setPrevalentDomainsToBlockButKeepCookiesFor(domainsToBlock.domainsToBlockButKeepCookiesFor);
+            storageSession->setDomainsWithUserInteractionAsFirstParty(domainsToBlock.domainsWithUserInteractionAsFirstParty);
         }
     }
 
diff --git a/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.h b/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.h
index 4164ab6..38b7c0e 100644
--- a/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.h
+++ b/Source/WebKit/NetworkProcess/Classifier/WebResourceLoadStatisticsStore.h
@@ -65,7 +65,6 @@
 enum class ShouldGrandfatherStatistics : bool;
 enum class ShouldIncludeLocalhost : bool { No, Yes };
 enum class EnableResourceLoadStatisticsDebugMode : bool { No, Yes };
-enum class EnableResourceLoadStatisticsNSURLSessionSwitching : bool { No, Yes };
 enum class WebsiteDataToRemove : uint8_t {
     All,
     AllButHttpOnlyCookies,
@@ -74,7 +73,8 @@
 struct RegistrableDomainsToBlockCookiesFor {
     Vector<WebCore::RegistrableDomain> domainsToBlockAndDeleteCookiesFor;
     Vector<WebCore::RegistrableDomain> domainsToBlockButKeepCookiesFor;
-    RegistrableDomainsToBlockCookiesFor isolatedCopy() const { return { domainsToBlockAndDeleteCookiesFor.isolatedCopy(), domainsToBlockButKeepCookiesFor.isolatedCopy() }; }
+    Vector<WebCore::RegistrableDomain> domainsWithUserInteractionAsFirstParty;
+    RegistrableDomainsToBlockCookiesFor isolatedCopy() const { return { domainsToBlockAndDeleteCookiesFor.isolatedCopy(), domainsToBlockButKeepCookiesFor.isolatedCopy(), domainsWithUserInteractionAsFirstParty.isolatedCopy() }; }
 };
 
 class WebResourceLoadStatisticsStore final : public ThreadSafeRefCounted<WebResourceLoadStatisticsStore, WTF::DestructionThread::Main> {
diff --git a/Source/WebKit/NetworkProcess/NetworkProcess.cpp b/Source/WebKit/NetworkProcess/NetworkProcess.cpp
index 810e748..d5575ce 100644
--- a/Source/WebKit/NetworkProcess/NetworkProcess.cpp
+++ b/Source/WebKit/NetworkProcess/NetworkProcess.cpp
@@ -1258,6 +1258,15 @@
     });
     completionHandler();
 }
+
+void NetworkProcess::setShouldBlockThirdPartyCookiesForTesting(PAL::SessionID sessionID, bool enabled, CompletionHandler<void()>&& completionHandler)
+{
+    if (auto* networkStorageSession = storageSession(sessionID))
+        networkStorageSession->setIsThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled(enabled);
+    else
+        ASSERT_NOT_REACHED();
+    completionHandler();
+}
 #endif // ENABLE(RESOURCE_LOAD_STATISTICS)
 
 bool NetworkProcess::sessionIsControlledByAutomation(PAL::SessionID sessionID) const
diff --git a/Source/WebKit/NetworkProcess/NetworkProcess.h b/Source/WebKit/NetworkProcess/NetworkProcess.h
index c89df84..b5db56f 100644
--- a/Source/WebKit/NetworkProcess/NetworkProcess.h
+++ b/Source/WebKit/NetworkProcess/NetworkProcess.h
@@ -266,6 +266,7 @@
     void hasIsolatedSession(PAL::SessionID, const WebCore::RegistrableDomain&, CompletionHandler<void(bool)>&&) const;
     bool isITPDatabaseEnabled() const { return m_isITPDatabaseEnabled; }
     void setShouldDowngradeReferrerForTesting(bool, CompletionHandler<void()>&&);
+    void setShouldBlockThirdPartyCookiesForTesting(PAL::SessionID, bool, CompletionHandler<void()>&&);
 #endif
 
     using CacheStorageRootPathCallback = CompletionHandler<void(String&&)>;
diff --git a/Source/WebKit/NetworkProcess/NetworkProcess.messages.in b/Source/WebKit/NetworkProcess/NetworkProcess.messages.in
index c35d113..41fea0df 100644
--- a/Source/WebKit/NetworkProcess/NetworkProcess.messages.in
+++ b/Source/WebKit/NetworkProcess/NetworkProcess.messages.in
@@ -137,6 +137,7 @@
     DeleteCookiesForTesting(PAL::SessionID sessionID, WebCore::RegistrableDomain domain, bool includeHttpOnlyCookies) -> () Async
     HasIsolatedSession(PAL::SessionID sessionID, WebCore::RegistrableDomain domain) -> (bool hasIsolatedSession) Async
     SetShouldDowngradeReferrerForTesting(bool enabled) -> () Async
+    SetShouldBlockThirdPartyCookiesForTesting(PAL::SessionID sessionID, bool enabled) -> () Async
 #endif
 
     SetSessionIsControlledByAutomation(PAL::SessionID sessionID, bool controlled);
diff --git a/Source/WebKit/NetworkProcess/NetworkSession.h b/Source/WebKit/NetworkProcess/NetworkSession.h
index 9102279..aa44058 100644
--- a/Source/WebKit/NetworkProcess/NetworkSession.h
+++ b/Source/WebKit/NetworkProcess/NetworkSession.h
@@ -93,11 +93,11 @@
     void notifyPageStatisticsTelemetryFinished(unsigned numberOfPrevalentResources, unsigned numberOfPrevalentResourcesWithUserInteraction, unsigned numberOfPrevalentResourcesWithoutUserInteraction, unsigned topPrevalentResourceWithUserInteractionDaysSinceUserInteraction, unsigned medianDaysSinceUserInteractionPrevalentResourceWithUserInteraction, unsigned top3NumberOfPrevalentResourcesWithUI, unsigned top3MedianSubFrameWithoutUI, unsigned top3MedianSubResourceWithoutUI, unsigned top3MedianUniqueRedirectsWithoutUI, unsigned top3MedianDataRecordsRemovedWithoutUI);
     bool enableResourceLoadStatisticsLogTestingEvent() const { return m_enableResourceLoadStatisticsLogTestingEvent; }
     void setResourceLoadStatisticsLogTestingEvent(bool log) { m_enableResourceLoadStatisticsLogTestingEvent = log; }
-    bool shouldIsolateSessionsForPrevalentTopFrames() const { return m_enableResourceLoadStatisticsNSURLSessionSwitching == EnableResourceLoadStatisticsNSURLSessionSwitching::Yes; }
     virtual bool hasIsolatedSession(const WebCore::RegistrableDomain) const { return false; }
     virtual void clearIsolatedSessions() { }
     void setShouldDowngradeReferrerForTesting(bool);
     bool shouldDowngradeReferrer() const;
+    void setShouldBlockThirdPartyCookiesForTesting(bool);
 #endif
     void storeAdClickAttribution(WebCore::AdClickAttribution&&);
     void handleAdClickAttributionConversion(WebCore::AdClickAttribution::Conversion&&, const URL& requestURL, const WebCore::ResourceRequest& redirectRequest);
@@ -140,7 +140,6 @@
     ShouldIncludeLocalhost m_shouldIncludeLocalhostInResourceLoadStatistics { ShouldIncludeLocalhost::Yes };
     EnableResourceLoadStatisticsDebugMode m_enableResourceLoadStatisticsDebugMode { EnableResourceLoadStatisticsDebugMode::No };
     WebCore::RegistrableDomain m_resourceLoadStatisticsManualPrevalentResource;
-    EnableResourceLoadStatisticsNSURLSessionSwitching m_enableResourceLoadStatisticsNSURLSessionSwitching { EnableResourceLoadStatisticsNSURLSessionSwitching::No };
     bool m_enableResourceLoadStatisticsLogTestingEvent;
     bool m_downgradeReferrer { true };
 #endif
diff --git a/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.cpp b/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.cpp
index cc14099..d8734b5 100644
--- a/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.cpp
+++ b/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.cpp
@@ -68,7 +68,7 @@
     encoder << shouldIncludeLocalhostInResourceLoadStatistics;
     encoder << enableResourceLoadStatisticsDebugMode;
     encoder << resourceLoadStatisticsManualPrevalentResource;
-    encoder << enableResourceLoadStatisticsNSURLSessionSwitching;
+    encoder << enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction;
 
     encoder << networkCacheDirectory << networkCacheDirectoryExtensionHandle;
 
@@ -199,9 +199,9 @@
     if (!resourceLoadStatisticsManualPrevalentResource)
         return WTF::nullopt;
 
-    Optional<bool> enableResourceLoadStatisticsNSURLSessionSwitching;
-    decoder >> enableResourceLoadStatisticsNSURLSessionSwitching;
-    if (!enableResourceLoadStatisticsNSURLSessionSwitching)
+    Optional<bool> enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction;
+    decoder >> enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction;
+    if (!enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction)
         return WTF::nullopt;
 
     Optional<String> networkCacheDirectory;
@@ -282,7 +282,7 @@
         , WTFMove(*enableResourceLoadStatisticsLogTestingEvent)
         , WTFMove(*shouldIncludeLocalhostInResourceLoadStatistics)
         , WTFMove(*enableResourceLoadStatisticsDebugMode)
-        , WTFMove(*enableResourceLoadStatisticsNSURLSessionSwitching)
+        , WTFMove(*enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction)
         , WTFMove(*deviceManagementRestrictionsEnabled)
         , WTFMove(*allLoadsBlockedByDeviceManagementRestrictionsForTesting)
         , WTFMove(*resourceLoadStatisticsManualPrevalentResource)
diff --git a/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.h b/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.h
index e801712..4cddb0e 100644
--- a/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.h
+++ b/Source/WebKit/NetworkProcess/NetworkSessionCreationParameters.h
@@ -85,7 +85,7 @@
     bool enableResourceLoadStatisticsLogTestingEvent { false };
     bool shouldIncludeLocalhostInResourceLoadStatistics { true };
     bool enableResourceLoadStatisticsDebugMode { false };
-    bool enableResourceLoadStatisticsNSURLSessionSwitching { true };
+    bool enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction { false };
     bool deviceManagementRestrictionsEnabled { false };
     bool allLoadsBlockedByDeviceManagementRestrictionsForTesting { false };
     WebCore::RegistrableDomain resourceLoadStatisticsManualPrevalentResource { };
diff --git a/Source/WebKit/NetworkProcess/cocoa/NetworkDataTaskCocoa.mm b/Source/WebKit/NetworkProcess/cocoa/NetworkDataTaskCocoa.mm
index 77a220f..39db8b4 100644
--- a/Source/WebKit/NetworkProcess/cocoa/NetworkDataTaskCocoa.mm
+++ b/Source/WebKit/NetworkProcess/cocoa/NetworkDataTaskCocoa.mm
@@ -213,7 +213,7 @@
     if (auto* networkStorageSession = session.networkStorageSession()) {
         if (!shouldBlockCookies)
             shouldBlockCookies = networkStorageSession->shouldBlockCookies(request, frameID, pageID);
-        needsIsolatedSession = session.shouldIsolateSessionsForPrevalentTopFrames() && networkStorageSession->shouldBlockThirdPartyCookiesButKeepFirstPartyCookiesFor(firstParty);
+        needsIsolatedSession = networkStorageSession->shouldBlockThirdPartyCookiesButKeepFirstPartyCookiesFor(firstParty);
     }
 #endif
     restrictRequestReferrerToOriginIfNeeded(request);
diff --git a/Source/WebKit/NetworkProcess/cocoa/NetworkSessionCocoa.mm b/Source/WebKit/NetworkProcess/cocoa/NetworkSessionCocoa.mm
index 00be2c2..fab6fce 100644
--- a/Source/WebKit/NetworkProcess/cocoa/NetworkSessionCocoa.mm
+++ b/Source/WebKit/NetworkProcess/cocoa/NetworkSessionCocoa.mm
@@ -1109,7 +1109,7 @@
     m_shouldIncludeLocalhostInResourceLoadStatistics = parameters.shouldIncludeLocalhostInResourceLoadStatistics ? ShouldIncludeLocalhost::Yes : ShouldIncludeLocalhost::No;
     m_enableResourceLoadStatisticsDebugMode = parameters.enableResourceLoadStatisticsDebugMode ? EnableResourceLoadStatisticsDebugMode::Yes : EnableResourceLoadStatisticsDebugMode::No;
     m_resourceLoadStatisticsManualPrevalentResource = parameters.resourceLoadStatisticsManualPrevalentResource;
-    m_enableResourceLoadStatisticsNSURLSessionSwitching = parameters.enableResourceLoadStatisticsNSURLSessionSwitching ? EnableResourceLoadStatisticsNSURLSessionSwitching::Yes : EnableResourceLoadStatisticsNSURLSessionSwitching::No;
+    storageSession->setIsThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled(parameters.enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction);
     setResourceLoadStatisticsEnabled(parameters.enableResourceLoadStatistics);
 #endif
 
diff --git a/Source/WebKit/Shared/WebPreferences.yaml b/Source/WebKit/Shared/WebPreferences.yaml
index 974618f..6659493 100644
--- a/Source/WebKit/Shared/WebPreferences.yaml
+++ b/Source/WebKit/Shared/WebPreferences.yaml
@@ -1765,12 +1765,11 @@
   webcoreBinding: RuntimeEnabledFeatures
   category: experimental
 
-IsITPSessionSwitchingEnabled:
+IsThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabled:
   type: bool
-  defaultValue: true
-  humanReadableName: "ITP Session Switching"
-  humanReadableDescription: "Enable session switching for domains classified by ITP"
-  webcoreBinding: RuntimeEnabledFeatures
+  defaultValue: false
+  humanReadableName: "Block 3rd-Party Cookies On Sites Without Interaction (ITP)"
+  humanReadableDescription: "Block all third-party cookies on websites without user interaction"
   category: internal
 
 IsLoggedInAPIEnabled:
diff --git a/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp b/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp
index d335060..7089f7e 100644
--- a/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp
+++ b/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.cpp
@@ -538,6 +538,17 @@
 #endif
 }
 
+void WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(WKWebsiteDataStoreRef dataStoreRef, bool enabled, void* context, WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTestingFunction completionHandler)
+{
+#if ENABLE(RESOURCE_LOAD_STATISTICS)
+    WebKit::toImpl(dataStoreRef)->setResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(enabled, [context, completionHandler] {
+        completionHandler(context);
+    });
+#else
+    completionHandler(context);
+#endif
+}
+
 void WKWebsiteDataStoreStatisticsResetToConsistentState(WKWebsiteDataStoreRef dataStoreRef, void* context, WKWebsiteDataStoreStatisticsResetToConsistentStateFunction completionHandler)
 {
 #if ENABLE(RESOURCE_LOAD_STATISTICS)
@@ -550,6 +561,7 @@
     store.resetCacheMaxAgeCapForPrevalentResources([callbackAggregator = callbackAggregator.copyRef()] { });
     store.resetCrossSiteLoadsWithLinkDecorationForTesting([callbackAggregator = callbackAggregator.copyRef()] { });
     store.setResourceLoadStatisticsShouldDowngradeReferrerForTesting(true, [callbackAggregator = callbackAggregator.copyRef()] { });
+    store.setResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(false, [callbackAggregator = callbackAggregator.copyRef()] { });
     store.resetParametersToDefaultValues([callbackAggregator = callbackAggregator.copyRef()] { });
     store.scheduleClearInMemoryAndPersistent(WebKit::ShouldGrandfatherStatistics::No, [callbackAggregator = callbackAggregator.copyRef()] { });
     store.setUseITPDatabase(false, [callbackAggregator = callbackAggregator.copyRef()] { });
diff --git a/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.h b/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.h
index ad5c2ce..65385f8 100644
--- a/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.h
+++ b/Source/WebKit/UIProcess/API/C/WKWebsiteDataStoreRef.h
@@ -117,6 +117,8 @@
 WK_EXPORT void WKWebsiteDataStoreStatisticsHasIsolatedSession(WKWebsiteDataStoreRef dataStoreRef, WKStringRef host, void* context, WKWebsiteDataStoreStatisticsHasIsolatedSessionFunction callback);
 typedef void (*WKWebsiteDataStoreSetResourceLoadStatisticsShouldDowngradeReferrerForTestingFunction)(void* functionContext);
 WK_EXPORT void WKWebsiteDataStoreSetResourceLoadStatisticsShouldDowngradeReferrerForTesting(WKWebsiteDataStoreRef dataStoreRef, bool enabled, void* context, WKWebsiteDataStoreSetResourceLoadStatisticsShouldDowngradeReferrerForTestingFunction completionHandler);
+typedef void (*WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTestingFunction)(void* functionContext);
+WK_EXPORT void WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(WKWebsiteDataStoreRef dataStoreRef, bool enabled, void* context, WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTestingFunction completionHandler);
 typedef void (*WKWebsiteDataStoreStatisticsResetToConsistentStateFunction)(void* functionContext);
 WK_EXPORT void WKWebsiteDataStoreStatisticsResetToConsistentState(WKWebsiteDataStoreRef dataStoreRef, void* context, WKWebsiteDataStoreStatisticsResetToConsistentStateFunction completionHandler);
 
diff --git a/Source/WebKit/UIProcess/Network/NetworkProcessProxy.cpp b/Source/WebKit/UIProcess/Network/NetworkProcessProxy.cpp
index 4585cff..6c190529 100644
--- a/Source/WebKit/UIProcess/Network/NetworkProcessProxy.cpp
+++ b/Source/WebKit/UIProcess/Network/NetworkProcessProxy.cpp
@@ -1054,6 +1054,16 @@
     
     sendWithAsyncReply(Messages::NetworkProcess::SetShouldDowngradeReferrerForTesting(enabled), WTFMove(completionHandler));
 }
+
+void NetworkProcessProxy::setShouldBlockThirdPartyCookiesForTesting(PAL::SessionID sessionID, bool enabled, CompletionHandler<void()>&& completionHandler)
+{
+    if (!canSendMessage()) {
+        completionHandler();
+        return;
+    }
+    
+    sendWithAsyncReply(Messages::NetworkProcess::SetShouldBlockThirdPartyCookiesForTesting(sessionID, enabled), WTFMove(completionHandler));
+}
 #endif // ENABLE(RESOURCE_LOAD_STATISTICS)
 
 void NetworkProcessProxy::sendProcessWillSuspendImminently()
diff --git a/Source/WebKit/UIProcess/Network/NetworkProcessProxy.h b/Source/WebKit/UIProcess/Network/NetworkProcessProxy.h
index 6ab2039..da4bed2 100644
--- a/Source/WebKit/UIProcess/Network/NetworkProcessProxy.h
+++ b/Source/WebKit/UIProcess/Network/NetworkProcessProxy.h
@@ -155,6 +155,7 @@
     void deleteWebsiteDataInUIProcessForRegistrableDomains(PAL::SessionID, OptionSet<WebsiteDataType>, OptionSet<WebsiteDataFetchOption>, Vector<RegistrableDomain>, CompletionHandler<void(HashSet<WebCore::RegistrableDomain>&&)>&&);
     void hasIsolatedSession(PAL::SessionID, const RegistrableDomain&, CompletionHandler<void(bool)>&&);
     void setShouldDowngradeReferrerForTesting(bool, CompletionHandler<void()>&&);
+    void setShouldBlockThirdPartyCookiesForTesting(PAL::SessionID, bool, CompletionHandler<void()>&&);
 #endif
 
     void processReadyToSuspend();
diff --git a/Source/WebKit/UIProcess/WebsiteData/Cocoa/WebsiteDataStoreCocoa.mm b/Source/WebKit/UIProcess/WebsiteData/Cocoa/WebsiteDataStoreCocoa.mm
index cd4ab9c..78c66a6 100644
--- a/Source/WebKit/UIProcess/WebsiteData/Cocoa/WebsiteDataStoreCocoa.mm
+++ b/Source/WebKit/UIProcess/WebsiteData/Cocoa/WebsiteDataStoreCocoa.mm
@@ -29,6 +29,7 @@
 #import "CookieStorageUtilsCF.h"
 #import "SandboxUtilities.h"
 #import "StorageManager.h"
+#import "WebPreferencesKeys.h"
 #import "WebResourceLoadStatisticsStore.h"
 #import "WebsiteDataStoreParameters.h"
 #import <WebCore/RegistrableDomain.h>
@@ -68,11 +69,12 @@
     NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
     bool shouldLogCookieInformation = false;
     bool enableResourceLoadStatisticsDebugMode = false;
-    bool enableResourceLoadStatisticsNSURLSessionSwitching = WebCore::RuntimeEnabledFeatures::sharedFeatures().isITPSessionSwitchingEnabled();
-    WebCore::RegistrableDomain resourceLoadStatisticsManualPrevalentResource { };
+    bool enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction = false;
     bool enableLegacyTLS = [defaults boolForKey:@"WebKitEnableLegacyTLS"];
+    WebCore::RegistrableDomain resourceLoadStatisticsManualPrevalentResource { };
 #if ENABLE(RESOURCE_LOAD_STATISTICS)
     enableResourceLoadStatisticsDebugMode = [defaults boolForKey:@"ITPDebugMode"];
+    enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction = [defaults boolForKey:[NSString stringWithFormat:@"InternalDebug%@", WebPreferencesKey::isThirdPartyCookieBlockingOnSitesWithoutUserInteractionEnabledKey().createCFString().get()]];
     auto* manualPrevalentResource = [defaults stringForKey:@"ITPManualPrevalentResource"];
     if (manualPrevalentResource) {
         URL url { URL(), manualPrevalentResource };
@@ -136,7 +138,7 @@
         hasStatisticsTestingCallback(),
         shouldIncludeLocalhostInResourceLoadStatistics,
         enableResourceLoadStatisticsDebugMode,
-        enableResourceLoadStatisticsNSURLSessionSwitching,
+        enableThirdPartyCookieBlockingOnSitesWithoutUserInteraction,
         m_configuration->deviceManagementRestrictionsEnabled(),
         m_configuration->allLoadsBlockedByDeviceManagementRestrictionsForTesting(),
         WTFMove(resourceLoadStatisticsManualPrevalentResource),
diff --git a/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.cpp b/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.cpp
index 3908d7b..14b60ae 100644
--- a/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.cpp
+++ b/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.cpp
@@ -1782,6 +1782,20 @@
     }
     ASSERT(!completionHandler);
 }
+
+void WebsiteDataStore::setResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(bool enabled, CompletionHandler<void()>&& completionHandler)
+{
+    auto callbackAggregator = CallbackAggregator::create(WTFMove(completionHandler));
+    
+    for (auto& processPool : processPools()) {
+        if (auto* networkProcess = processPool->networkProcess()) {
+            networkProcess->setShouldBlockThirdPartyCookiesForTesting(m_sessionID, enabled, [callbackAggregator = callbackAggregator.copyRef()] { });
+            ASSERT(processPools().size() == 1);
+            break;
+        }
+    }
+    ASSERT(!completionHandler);
+}
 #endif // ENABLE(RESOURCE_LOAD_STATISTICS)
 
 void WebsiteDataStore::setCacheMaxAgeCapForPrevalentResources(Seconds seconds, CompletionHandler<void()>&& completionHandler)
diff --git a/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.h b/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.h
index 930e305..f9a21db 100644
--- a/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.h
+++ b/Source/WebKit/UIProcess/WebsiteData/WebsiteDataStore.h
@@ -192,6 +192,7 @@
     void hasLocalStorageForTesting(const URL&, CompletionHandler<void(bool)>&&) const;
     void hasIsolatedSessionForTesting(const URL&, CompletionHandler<void(bool)>&&) const;
     void setResourceLoadStatisticsShouldDowngradeReferrerForTesting(bool, CompletionHandler<void()>&&);
+    void setResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(bool, CompletionHandler<void()>&&);
 #endif
     void setCacheMaxAgeCapForPrevalentResources(Seconds, CompletionHandler<void()>&&);
     void resetCacheMaxAgeCapForPrevalentResources(CompletionHandler<void()>&&);
diff --git a/Tools/ChangeLog b/Tools/ChangeLog
index f402594..a1b8ff4 100644
--- a/Tools/ChangeLog
+++ b/Tools/ChangeLog
@@ -1,3 +1,29 @@
+2019-10-16  John Wilander  <wilander@apple.com>
+
+        Resource Load Statistics (experimental): Block all third-party cookies on websites without prior user interaction
+        https://bugs.webkit.org/show_bug.cgi?id=203017
+        <rdar://problem/56262708>
+
+        Reviewed by Alex Christensen.
+
+        These changes are test infrastructure to be able to toggle the function
+        through testRunner.setStatisticsShouldBlockThirdPartyCookies().
+
+        * WebKitTestRunner/InjectedBundle/Bindings/TestRunner.idl:
+        * WebKitTestRunner/InjectedBundle/InjectedBundle.cpp:
+        (WTR::InjectedBundle::didReceiveMessageToPage):
+        * WebKitTestRunner/InjectedBundle/TestRunner.cpp:
+        (WTR::TestRunner::setStatisticsShouldBlockThirdPartyCookies):
+        (WTR::TestRunner::statisticsCallDidSetShouldBlockThirdPartyCookiesCallback):
+        * WebKitTestRunner/InjectedBundle/TestRunner.h:
+        * WebKitTestRunner/TestController.cpp:
+        (WTR::TestController::setStatisticsShouldBlockThirdPartyCookies):
+        * WebKitTestRunner/TestController.h:
+        * WebKitTestRunner/TestInvocation.cpp:
+        (WTR::TestInvocation::didReceiveSynchronousMessageFromInjectedBundle):
+        (WTR::TestInvocation::didSetShouldBlockThirdPartyCookies):
+        * WebKitTestRunner/TestInvocation.h:
+
 2019-10-16  Kate Cheney  <katherine_cheney@apple.com>
 
         WKWebsiteDataStoreStatisticsResetToConsistentState() should call store.setUseITPDatabase(false)
diff --git a/Tools/WebKitTestRunner/InjectedBundle/Bindings/TestRunner.idl b/Tools/WebKitTestRunner/InjectedBundle/Bindings/TestRunner.idl
index e26b4fa..faef0a0 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/Bindings/TestRunner.idl
+++ b/Tools/WebKitTestRunner/InjectedBundle/Bindings/TestRunner.idl
@@ -341,6 +341,7 @@
     void statisticsResetToConsistentState(object completionHandler);
     boolean hasStatisticsIsolatedSession(DOMString hostName);
     void setStatisticsShouldDowngradeReferrer(boolean value, object callback);
+    void setStatisticsShouldBlockThirdPartyCookies(boolean value, object callback);
 
     // Injected bundle form client.
     void installTextDidChangeInTextFieldCallback(object callback);
diff --git a/Tools/WebKitTestRunner/InjectedBundle/InjectedBundle.cpp b/Tools/WebKitTestRunner/InjectedBundle/InjectedBundle.cpp
index e7ad015..f52ed1a 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/InjectedBundle.cpp
+++ b/Tools/WebKitTestRunner/InjectedBundle/InjectedBundle.cpp
@@ -332,6 +332,11 @@
         return;
     }
 
+    if (WKStringIsEqualToUTF8CString(messageName, "CallDidSetShouldBlockThirdPartyCookies")) {
+        m_testRunner->statisticsCallDidSetShouldBlockThirdPartyCookiesCallback();
+        return;
+    }
+
     if (WKStringIsEqualToUTF8CString(messageName, "CallDidResetStatisticsToConsistentState")) {
         m_testRunner->statisticsCallDidResetToConsistentStateCallback();
         return;
diff --git a/Tools/WebKitTestRunner/InjectedBundle/TestRunner.cpp b/Tools/WebKitTestRunner/InjectedBundle/TestRunner.cpp
index ba5993c7a..b4f0b4b 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/TestRunner.cpp
+++ b/Tools/WebKitTestRunner/InjectedBundle/TestRunner.cpp
@@ -743,6 +743,7 @@
     StatisticsDidResetToConsistentStateCallbackID,
     StatisticsDidSetBlockCookiesForHostCallbackID,
     StatisticsDidSetShouldDowngradeReferrerCallbackID,
+    StatisticsDidSetShouldBlockThirdPartyCookiesCallbackID,
     AllStorageAccessEntriesCallbackID,
     DidRemoveAllSessionCredentialsCallbackID,
     GetApplicationManifestCallbackID,
@@ -2208,6 +2209,23 @@
     callTestRunnerCallback(StatisticsDidSetShouldDowngradeReferrerCallbackID);
 }
 
+void TestRunner::setStatisticsShouldBlockThirdPartyCookies(bool value, JSValueRef completionHandler)
+{
+    if (m_hasSetBlockThirdPartyCookiesCallback)
+        return;
+    
+    cacheTestRunnerCallback(StatisticsDidSetShouldBlockThirdPartyCookiesCallbackID, completionHandler);
+    WKRetainPtr<WKStringRef> messageName = adoptWK(WKStringCreateWithUTF8CString("SetStatisticsShouldBlockThirdPartyCookies"));
+    WKRetainPtr<WKBooleanRef> messageBody = adoptWK(WKBooleanCreate(value));
+    WKBundlePostSynchronousMessage(InjectedBundle::singleton().bundle(), messageName.get(), messageBody.get(), nullptr);
+    m_hasSetBlockThirdPartyCookiesCallback = true;
+}
+
+void TestRunner::statisticsCallDidSetShouldBlockThirdPartyCookiesCallback()
+{
+    callTestRunnerCallback(StatisticsDidSetShouldBlockThirdPartyCookiesCallbackID);
+}
+
 void TestRunner::statisticsCallClearThroughWebsiteDataRemovalCallback()
 {
     callTestRunnerCallback(StatisticsDidClearThroughWebsiteDataRemovalCallbackID);
diff --git a/Tools/WebKitTestRunner/InjectedBundle/TestRunner.h b/Tools/WebKitTestRunner/InjectedBundle/TestRunner.h
index c1f124f..e0394e6 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/TestRunner.h
+++ b/Tools/WebKitTestRunner/InjectedBundle/TestRunner.h
@@ -440,6 +440,8 @@
     bool hasStatisticsIsolatedSession(JSStringRef hostName);
     void setStatisticsShouldDowngradeReferrer(bool, JSValueRef callback);
     void statisticsCallDidSetShouldDowngradeReferrerCallback();
+    void setStatisticsShouldBlockThirdPartyCookies(bool, JSValueRef callback);
+    void statisticsCallDidSetShouldBlockThirdPartyCookiesCallback();
     void statisticsResetToConsistentState(JSValueRef completionHandler);
     void statisticsCallDidResetToConsistentStateCallback();
 
@@ -573,6 +575,7 @@
     bool m_userStyleSheetEnabled { false };
     bool m_dumpAllHTTPRedirectedResponseHeaders { false };
     bool m_hasSetDowngradeReferrerCallback { false };
+    bool m_hasSetBlockThirdPartyCookiesCallback { false };
 };
 
 } // namespace WTR
diff --git a/Tools/WebKitTestRunner/TestController.cpp b/Tools/WebKitTestRunner/TestController.cpp
index 4ba4916..ea9c6a5 100644
--- a/Tools/WebKitTestRunner/TestController.cpp
+++ b/Tools/WebKitTestRunner/TestController.cpp
@@ -3555,6 +3555,14 @@
     m_currentInvocation->didSetShouldDowngradeReferrer();
 }
 
+void TestController::setStatisticsShouldBlockThirdPartyCookies(bool value)
+{
+    ResourceStatisticsCallbackContext context(*this);
+    WKWebsiteDataStoreSetResourceLoadStatisticsShouldBlockThirdPartyCookiesForTesting(TestController::websiteDataStore(), value, &context, resourceStatisticsVoidResultCallback);
+    runUntil(context.done, noTimeout);
+    m_currentInvocation->didSetShouldBlockThirdPartyCookies();
+}
+
 void TestController::statisticsResetToConsistentState()
 {
     ResourceStatisticsCallbackContext context(*this);
diff --git a/Tools/WebKitTestRunner/TestController.h b/Tools/WebKitTestRunner/TestController.h
index 4bf9023..680d2e2 100644
--- a/Tools/WebKitTestRunner/TestController.h
+++ b/Tools/WebKitTestRunner/TestController.h
@@ -252,6 +252,7 @@
     void setStatisticsCacheMaxAgeCap(double seconds);
     bool hasStatisticsIsolatedSession(WKStringRef hostName);
     void setStatisticsShouldDowngradeReferrer(bool value);
+    void setStatisticsShouldBlockThirdPartyCookies(bool value);
     void statisticsResetToConsistentState();
 
     void getAllStorageAccessEntries();
diff --git a/Tools/WebKitTestRunner/TestInvocation.cpp b/Tools/WebKitTestRunner/TestInvocation.cpp
index 8fe9279..3c6269c 100644
--- a/Tools/WebKitTestRunner/TestInvocation.cpp
+++ b/Tools/WebKitTestRunner/TestInvocation.cpp
@@ -1542,6 +1542,13 @@
         return nullptr;
     }
     
+    if (WKStringIsEqualToUTF8CString(messageName, "SetStatisticsShouldBlockThirdPartyCookies")) {
+        ASSERT(WKGetTypeID(messageBody) == WKBooleanGetTypeID());
+        WKBooleanRef value = static_cast<WKBooleanRef>(messageBody);
+        TestController::singleton().setStatisticsShouldBlockThirdPartyCookies(WKBooleanGetValue(value));
+        return nullptr;
+    }
+    
     if (WKStringIsEqualToUTF8CString(messageName, "RemoveAllSessionCredentials")) {
         TestController::singleton().removeAllSessionCredentials();
         return nullptr;
@@ -1825,6 +1832,12 @@
     WKPagePostMessageToInjectedBundle(TestController::singleton().mainWebView()->page(), messageName.get(), 0);
 }
 
+void TestInvocation::didSetShouldBlockThirdPartyCookies()
+{
+    WKRetainPtr<WKStringRef> messageName = adoptWK(WKStringCreateWithUTF8CString("CallDidSetShouldBlockThirdPartyCookies"));
+    WKPagePostMessageToInjectedBundle(TestController::singleton().mainWebView()->page(), messageName.get(), nullptr);
+}
+
 void TestInvocation::didResetStatisticsToConsistentState()
 {
     WKRetainPtr<WKStringRef> messageName = adoptWK(WKStringCreateWithUTF8CString("CallDidResetStatisticsToConsistentState"));
diff --git a/Tools/WebKitTestRunner/TestInvocation.h b/Tools/WebKitTestRunner/TestInvocation.h
index a265eb9..7806fa2 100644
--- a/Tools/WebKitTestRunner/TestInvocation.h
+++ b/Tools/WebKitTestRunner/TestInvocation.h
@@ -74,6 +74,7 @@
 
     void didClearStatisticsThroughWebsiteDataRemoval();
     void didSetShouldDowngradeReferrer();
+    void didSetShouldBlockThirdPartyCookies();
     void didResetStatisticsToConsistentState();
     void didSetBlockCookiesForHost();
     void didSetStatisticsDebugMode();