[wrapper-tracing] Avoid firing the write barrier after TraceEpilogue

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WrapperVisitor_h
 #define WrapperVisitor_h
 
 #include "platform/PlatformExport.h"
 #include "wtf/Allocator.h"
 
@@ skipping 87 matching lines @@
                   "dispatchTraceWrappers in WrapperVisitor.h");
 
     if (!traceable) {
       return;
     }
 
     if (TraceTrait<T>::heapObjectHeader(traceable)->isWrapperHeaderMarked()) {
       return;
     }
 
-    TraceTrait<T>::markWrapperNoTracing(this, traceable);
-    pushToMarkingDeque(TraceTrait<T>::traceMarkedWrapper,
-                       TraceTrait<T>::heapObjectHeader, traceable);
+    if (pushToMarkingDeque(TraceTrait<T>::traceMarkedWrapper,
+                           TraceTrait<T>::heapObjectHeader, traceable)) {
+      TraceTrait<T>::markWrapperNoTracing(this, traceable);
+    }
   }
 
   /**
    * Trace all wrappers of |t|.
    *
    * If you cannot use TraceWrapperMember & the corresponding traceWrappers()
    * for some reason (e.g., due to sizeof(TraceWrapperMember)), you can use
    * Member and |traceWrappersWithManualWriteBarrier()|. See below.
    */
   template <typename T>
@@ skipping 35 matching lines @@
 
   virtual bool markWrapperHeader(HeapObjectHeader*) const = 0;
 
   virtual void markWrappersInAllWorlds(const ScriptWrappable*) const = 0;
 
   void markWrappersInAllWorlds(const void*) const {
     // Empty handler used for WRAPPER_VISITOR_SPECIAL_CLASSES. These types
     // don't require marking wrappers in all worlds, so just nop on those.
   }
 
-  virtual void pushToMarkingDeque(
+  // Returns true if pushing to the marking deque was successful.
+  virtual bool pushToMarkingDeque(
       void (*traceWrappersCallback)(const WrapperVisitor*, const void*),
       HeapObjectHeader* (*heapObjectHeaderCallback)(const void*),
       const void*) const = 0;
 };
 
 #define SPECIALIZE_WRAPPER_TRACING_MARK_TRAIT(ClassName) \
   template <>                                            \
   class CanTraceWrappers<ClassName, false> {             \
    public:                                               \
     static const bool value = true;                      \
   };
 
 WRAPPER_VISITOR_SPECIAL_CLASSES(SPECIALIZE_WRAPPER_TRACING_MARK_TRAIT)
 
 #undef SPECIALIZE_WRAPPER_TRACING_MARK_TRAIT
 
 }  // namespace blink
 
 #endif  // WrapperVisitor_h