diff --git a/Source/WebCore/css/DOMWindowCSS.cpp b/Source/WebCore/css/DOMWindowCSS.cpp
new file mode 100644
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+++ b/Source/WebCore/css/DOMWindowCSS.cpp
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+/*
+ * Copyright (C) 2012 Motorola Mobility Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above
+ *    copyright notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Motorola Mobility Inc. nor the names of its
+ *    contributors may be used to endorse or promote products derived from this
+ *    software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "DOMWindowCSS.h"
+
+#if ENABLE(CSS3_CONDITIONAL_RULES)
+
+#include "CSSParser.h"
+#include "StylePropertySet.h"
+#include <wtf/text/WTFString.h>
+
+namespace WebCore {
+
+PassRefPtr<DOMWindowCSS> DOMWindowCSS::create()
+{
+    return adoptRef(new DOMWindowCSS());
+}
+
+static String valueWithoutImportant(const String& value)
+{
+    if (!value.endsWith("important", false))
+        return value;
+
+    String newValue = value;
+    int bangIndex = newValue.length() - 9 - 1;
+    if (newValue[bangIndex] == ' ')
+        bangIndex--;
+    newValue = newValue.left(bangIndex);
+
+    return newValue;
+}
+
+bool DOMWindowCSS::supports(const String& property, const String& value) const
+{
+    CSSPropertyID propertyID = cssPropertyID(property.stripWhiteSpace());
+
+    if (propertyID == CSSPropertyInvalid)
+        return false;
+
+    // CSSParser::parseValue() won't work correctly if !important is present,
+    // so just get rid of it. It doesn't matter to supports() if it's actually
+    // there or not, provided how it's specified in the value is correct.
+    String normalizedValue = value.stripWhiteSpace().simplifyWhiteSpace();
+    normalizedValue = valueWithoutImportant(normalizedValue);
+
+    if (normalizedValue.isEmpty())
+        return false;
+
+    RefPtr<StylePropertySet> dummyStyle = StylePropertySet::create();
+    return CSSParser::parseValue(dummyStyle.get(), propertyID, normalizedValue, false, CSSStrictMode, 0);
+}
+
+bool DOMWindowCSS::supports(const String& conditionText) const
+{
+    CSSParserContext context(CSSStrictMode);
+    CSSParser parser(context);
+    return parser.parseSupportsCondition(conditionText);
+}
+
+}
+
+#endif