Fix perf regression in blink_perf.shadow_dom.

The static strings were destructed at the exit instead of leaked,
causing performance regression. Since the GCInfo objects are leaked,
holding a reference in the struct will leak the strings.

BUG=520948

Review URL: https://codereview.chromium.org/1300263003

git-svn-id: svn://svn.chromium.org/blink/trunk@200944 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/heap/GCInfo.h

@@ -111,16 +111,15 @@ extern PLATFORM_EXPORT GCInfo const** s_gcInfoTable;
 // reachable. There is a GCInfo struct for each class that directly
 // inherits from GarbageCollected or GarbageCollectedFinalized.
 struct GCInfo {
-    using GetClassNameCallback = const String& (*)();
-
     bool hasFinalizer() const { return m_nonTrivialFinalizer; }
     bool hasVTable() const { return m_hasVTable; }
-    const String& className() const { return m_classNameGetter(); }
+    const String& className() const { return m_className; }
     TraceCallback m_trace;
     FinalizationCallback m_finalize;
     bool m_nonTrivialFinalizer;
     bool m_hasVTable;
-    GetClassNameCallback m_classNameGetter;
+    // |m_className| is held as a reference to prevent dtor being called at exit.
+    const String& m_className;
 };
 
 #if ENABLE(ASSERT)
@@ -172,7 +171,7 @@ struct GCInfoAtBase {
             FinalizerTrait<T>::finalize,
             FinalizerTrait<T>::nonTrivialFinalizer,
             WTF::IsPolymorphic<T>::value,
-            TypenameStringTrait<T>::get
+            TypenameStringTrait<T>::get()
         };
         RETURN_GCINFO_INDEX();
     }

third_party/WebKit/Source/platform/heap/Visitor.h

@@ -41,11 +41,10 @@
 #include "wtf/Forward.h"
 #include "wtf/HashMap.h"
 #include "wtf/HashTraits.h"
-#include "wtf/TypeTraits.h"
-#if ENABLE(GC_PROFILING)
 #include "wtf/InstanceCounter.h"
+#include "wtf/Threading.h"
+#include "wtf/TypeTraits.h"
 #include "wtf/text/WTFString.h"
-#endif
 
 namespace blink {
 
@@ -391,7 +390,7 @@ struct TypenameStringTrait {
     // This method is not thread safe.
     static const String& get()
     {
-        DEFINE_STATIC_LOCAL(String, typenameString, (WTF::extractTypeNameFromFunctionName(WTF::extractNameFunction<T>())));
+        AtomicallyInitializedStaticReference(AtomicString, typenameString, new AtomicString(WTF::extractTypeNameFromFunctionName(WTF::extractNameFunction<T>())));
         return typenameString;
     }
 };