diff --git a/Source/JavaScriptCore/ChangeLog b/Source/JavaScriptCore/ChangeLog
index e3f3c2e..0a23900 100644
--- a/Source/JavaScriptCore/ChangeLog
+++ b/Source/JavaScriptCore/ChangeLog
@@ -1,3 +1,16 @@
+2011-03-03  Timothy Hatcher  <timothy@apple.com>
+
+        Make APIShims usable from WebCore.
+
+        Reviewed by Oliver Hunt.
+
+        * ForwardingHeaders/JavaScriptCore/APIShims.h: Added.
+        * GNUmakefile.am:
+        * JavaScriptCore.exp:
+        * JavaScriptCore.gypi:
+        * JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCoreGenerated.make:
+        * JavaScriptCore.xcodeproj/project.pbxproj:
+
 2011-03-03  Peter Varga  <pvarga@webkit.org>
 
         Reviewed by Oliver Hunt.
diff --git a/Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/APIShims.h b/Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/APIShims.h
new file mode 100644
index 0000000..92e712a
--- /dev/null
+++ b/Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/APIShims.h
@@ -0,0 +1 @@
+#include <JavaScriptCore/API/APIShims.h>
diff --git a/Source/JavaScriptCore/GNUmakefile.am b/Source/JavaScriptCore/GNUmakefile.am
index 1afb96c..babac89 100644
--- a/Source/JavaScriptCore/GNUmakefile.am
+++ b/Source/JavaScriptCore/GNUmakefile.am
@@ -122,6 +122,7 @@
 	Source/JavaScriptCore/debugger/Debugger.cpp \
 	Source/JavaScriptCore/debugger/Debugger.h \
 	Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/APICast.h \
+	Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/APIShims.h \
 	Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/JavaScriptCore.h \
 	Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/JavaScript.h \
 	Source/JavaScriptCore/ForwardingHeaders/JavaScriptCore/JSBase.h \
diff --git a/Source/JavaScriptCore/JavaScriptCore.exp b/Source/JavaScriptCore/JavaScriptCore.exp
index 11c41ca..6baa4d5 100644
--- a/Source/JavaScriptCore/JavaScriptCore.exp
+++ b/Source/JavaScriptCore/JavaScriptCore.exp
@@ -184,6 +184,7 @@
 __ZN3JSC17constructFunctionEPNS_9ExecStateERKNS_7ArgListERKNS_10IdentifierERKNS_7UStringEi
 __ZN3JSC17createSyntaxErrorEPNS_9ExecStateERKNS_7UStringE
 __ZN3JSC18DebuggerActivationC1ERNS_12JSGlobalDataEPNS_8JSObjectE
+__ZN3JSC18MachineStackMarker14registerThreadEv
 __ZN3JSC18PropertyDescriptor11setWritableEb
 __ZN3JSC18PropertyDescriptor12setUndefinedEv
 __ZN3JSC18PropertyDescriptor13setDescriptorENS_7JSValueEj
@@ -209,6 +210,7 @@
 __ZN3JSC25evaluateInGlobalCallFrameERKNS_7UStringERNS_7JSValueEPNS_14JSGlobalObjectE
 __ZN3JSC35createInterruptedExecutionExceptionEPNS_12JSGlobalDataE
 __ZN3JSC3NaNE
+__ZN3JSC4Heap16activityCallbackEv
 __ZN3JSC4Heap16allocateSlowCaseEm
 __ZN3JSC4Heap16objectTypeCountsEv
 __ZN3JSC4Heap17collectAllGarbageEv
diff --git a/Source/JavaScriptCore/JavaScriptCore.gypi b/Source/JavaScriptCore/JavaScriptCore.gypi
index 4e33fe2..09972e1 100644
--- a/Source/JavaScriptCore/JavaScriptCore.gypi
+++ b/Source/JavaScriptCore/JavaScriptCore.gypi
@@ -15,6 +15,7 @@
         # These headers are part of JavaScriptCore's private API in the Apple Mac build.
         'javascriptcore_privateheader_files': [
             'API/APICast.h',
+            'API/APIShims.h',
             'API/JSBasePrivate.h',
             'API/JSContextRefPrivate.h',
             'API/JSObjectRefPrivate.h',
@@ -251,6 +252,7 @@
             'API/OpaqueJSString.cpp',
             'AllInOneFile.cpp',
             'ForwardingHeaders/JavaScriptCore/APICast.h',
+            'ForwardingHeaders/JavaScriptCore/APIShims.h',
             'ForwardingHeaders/JavaScriptCore/JSBase.h',
             'ForwardingHeaders/JavaScriptCore/JSContextRef.h',
             'ForwardingHeaders/JavaScriptCore/JSObjectRef.h',
diff --git a/Source/JavaScriptCore/JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCoreGenerated.make b/Source/JavaScriptCore/JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCoreGenerated.make
index db2a175..ba95c46 100644
--- a/Source/JavaScriptCore/JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCoreGenerated.make
+++ b/Source/JavaScriptCore/JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCoreGenerated.make
@@ -6,6 +6,7 @@
 !ENDIF
     -mkdir 2>NUL "%ConfigurationBuildDir%\include\JavaScriptCore"
     xcopy /y /d "..\..\API\APICast.h" "%ConfigurationBuildDir%\include\JavaScriptCore"
+    xcopy /y /d "..\..\API\APIShims.h" "%ConfigurationBuildDir%\include\JavaScriptCore"
     xcopy /y /d "..\..\API\JavaScript.h" "%ConfigurationBuildDir%\include\JavaScriptCore"
     xcopy /y /d "..\..\API\JSBase.h" "%ConfigurationBuildDir%\include\JavaScriptCore"
     xcopy /y /d "..\..\API\JSContextRef.h" "%ConfigurationBuildDir%\include\JavaScriptCore"
diff --git a/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj b/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
index 47eb4e2..08622bb 100644
--- a/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
+++ b/Source/JavaScriptCore/JavaScriptCore.xcodeproj/project.pbxproj
@@ -225,7 +225,7 @@
 		86438FC41265503E00E0DFCA /* StringBuilder.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86438FC31265503E00E0DFCA /* StringBuilder.cpp */; };
 		86565742115BE3DA00291F40 /* CString.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86565740115BE3DA00291F40 /* CString.cpp */; };
 		86565743115BE3DA00291F40 /* CString.h in Headers */ = {isa = PBXBuildFile; fileRef = 86565741115BE3DA00291F40 /* CString.h */; settings = {ATTRIBUTES = (Private, ); }; };
-		865F408810E7D56300947361 /* APIShims.h in Headers */ = {isa = PBXBuildFile; fileRef = 865F408710E7D56300947361 /* APIShims.h */; };
+		865F408810E7D56300947361 /* APIShims.h in Headers */ = {isa = PBXBuildFile; fileRef = 865F408710E7D56300947361 /* APIShims.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		86676D5211FED9BC004B6863 /* BumpPointerAllocator.h in Headers */ = {isa = PBXBuildFile; fileRef = 86676D4D11FED55D004B6863 /* BumpPointerAllocator.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		86704B4212DB8A8100A9FE7B /* YarrSyntaxChecker.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 86704B4012DB8A8100A9FE7B /* YarrSyntaxChecker.cpp */; };
 		86704B4312DB8A8100A9FE7B /* YarrSyntaxChecker.h in Headers */ = {isa = PBXBuildFile; fileRef = 86704B4112DB8A8100A9FE7B /* YarrSyntaxChecker.h */; };
@@ -555,7 +555,7 @@
 		BCFD8C930EEB2EE700283848 /* JumpTable.h in Headers */ = {isa = PBXBuildFile; fileRef = BCFD8C910EEB2EE700283848 /* JumpTable.h */; };
 		C0A272630E50A06300E96E15 /* NotFound.h in Headers */ = {isa = PBXBuildFile; fileRef = C0A2723F0E509F1E00E96E15 /* NotFound.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		DD377CBC12072C18006A2517 /* Bitmap.h in Headers */ = {isa = PBXBuildFile; fileRef = DD377CBB12072C18006A2517 /* Bitmap.h */; settings = {ATTRIBUTES = (Private, ); }; };
-		DDF7ABD411F60ED200108E36 /* GCActivityCallback.h in Headers */ = {isa = PBXBuildFile; fileRef = DDF7ABD211F60ED200108E36 /* GCActivityCallback.h */; };
+		DDF7ABD411F60ED200108E36 /* GCActivityCallback.h in Headers */ = {isa = PBXBuildFile; fileRef = DDF7ABD211F60ED200108E36 /* GCActivityCallback.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		DDF7ABD511F60ED200108E36 /* GCActivityCallbackCF.cpp in Sources */ = {isa = PBXBuildFile; fileRef = DDF7ABD311F60ED200108E36 /* GCActivityCallbackCF.cpp */; };
 		E124A8F70E555775003091F1 /* OpaqueJSString.h in Headers */ = {isa = PBXBuildFile; fileRef = E124A8F50E555775003091F1 /* OpaqueJSString.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		E124A8F80E555775003091F1 /* OpaqueJSString.cpp in Sources */ = {isa = PBXBuildFile; fileRef = E124A8F60E555775003091F1 /* OpaqueJSString.cpp */; };
diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 4d978db..b7d7803 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,16 @@
+2011-03-03  Timothy Hatcher  <timothy@apple.com>
+
+        Use APIEntryShim instead of JSLock in SerializedScriptValue to allow it to be used
+        by contexts not created by WebCore.
+
+        https://webkit.org/b/55642
+
+        Reviewed by Oliver Hunt.
+
+        * bindings/js/SerializedScriptValue.cpp:
+        (WebCore::SerializedScriptValue::create): Use APIEntryShim instead of JSLock.
+        (WebCore::SerializedScriptValue::deserialize): Ditto.
+
 2011-03-03  Alexey Proskuryakov  <ap@apple.com>
 
         Reviewed by Darin Adler.
diff --git a/Source/WebCore/bindings/js/SerializedScriptValue.cpp b/Source/WebCore/bindings/js/SerializedScriptValue.cpp
index 41ad198..b3d07ca 100644
--- a/Source/WebCore/bindings/js/SerializedScriptValue.cpp
+++ b/Source/WebCore/bindings/js/SerializedScriptValue.cpp
@@ -39,10 +39,10 @@
 #include "SharedBuffer.h"
 #include <limits>
 #include <JavaScriptCore/APICast.h>
+#include <JavaScriptCore/APIShims.h>
 #include <runtime/DateInstance.h>
 #include <runtime/Error.h>
 #include <runtime/ExceptionHelpers.h>
-#include <runtime/JSLock.h>
 #include <runtime/PropertyNameArray.h>
 #include <runtime/RegExp.h>
 #include <runtime/RegExpObject.h>
@@ -1381,8 +1381,8 @@
 
 PassRefPtr<SerializedScriptValue> SerializedScriptValue::create(JSContextRef originContext, JSValueRef apiValue, JSValueRef* exception)
 {
-    JSLock lock(SilenceAssertionsOnly);
     ExecState* exec = toJS(originContext);
+    APIEntryShim entryShim(exec);
     JSValue value = toJS(exec, apiValue);
     PassRefPtr<SerializedScriptValue> serializedValue = SerializedScriptValue::create(exec, value);
     if (exec->hadException()) {
@@ -1407,8 +1407,8 @@
 
 JSValueRef SerializedScriptValue::deserialize(JSContextRef destinationContext, JSValueRef* exception)
 {
-    JSLock lock(SilenceAssertionsOnly);
     ExecState* exec = toJS(destinationContext);
+    APIEntryShim entryShim(exec);
     JSValue value = deserialize(exec, exec->lexicalGlobalObject());
     if (exec->hadException()) {
         if (exception)