Turn MQ classes into thread safe

Source/core/css/MediaQueryExp.h

Index: Source/core/css/MediaQueryExp.h
diff --git a/Source/core/css/MediaQueryExp.h b/Source/core/css/MediaQueryExp.h
index 4717180475c376437e01ab67321eb596dab3e08a..e2549f64abb3c834fb5f634e0e0e2dc73472f246 100644
--- a/Source/core/css/MediaQueryExp.h
+++ b/Source/core/css/MediaQueryExp.h
@@ -33,7 +33,6 @@
 #include "core/css/CSSValue.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/RefPtr.h"
-#include "wtf/text/AtomicString.h"
 
 namespace WebCore {
 class CSSParserValueList;
@@ -41,16 +40,16 @@ class CSSParserValueList;
 class MediaQueryExp : public NoBaseWillBeGarbageCollectedFinalized<MediaQueryExp> {
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED;
 public:
-    static PassOwnPtrWillBeRawPtr<MediaQueryExp> create(const AtomicString& mediaFeature, CSSParserValueList*);
+    static PassOwnPtrWillBeRawPtr<MediaQueryExp> create(const String& mediaFeature, CSSParserValueList*);
     ~MediaQueryExp();
 
-    AtomicString mediaFeature() const { return m_mediaFeature; }
+    String mediaFeature() const { return m_mediaFeature; }

[abarth-chromium, 2014/03/06 08:03:57]

This can return a const String&

 
     CSSValue* value() const { return m_value.get(); }
 
     bool operator==(const MediaQueryExp& other) const
     {
-        return (other.m_mediaFeature == m_mediaFeature)
+        return (other.m_mediaFeatureHash == m_mediaFeatureHash)

[abarth-chromium, 2014/03/06 08:03:57]

Why do you need a hash?

Don't you need to check m_mediaFeature in addition to the hash?

             && ((!other.m_value && !m_value)
                 || (other.m_value && m_value && other.m_value->equals(*m_value)));
     }
@@ -66,9 +65,10 @@ public:
     MediaQueryExp(const MediaQueryExp& other);
 
 private:
-    MediaQueryExp(const AtomicString& mediaFeature, PassRefPtrWillBeRawPtr<CSSValue>);
+    MediaQueryExp(StringImpl*, PassRefPtrWillBeRawPtr<CSSValue>);

[abarth-chromium, 2014/03/06 08:03:57]

Why not const String& ?

 
-    AtomicString m_mediaFeature;
+    String m_mediaFeature;
+    unsigned m_mediaFeatureHash;

[abarth-chromium, 2014/03/06 08:03:57]

Is this needed for performance?

     RefPtrWillBeMember<CSSValue> m_value;
 };