[wrapper-tracing] Fix write barrier in copy ctor

third_party/WebKit/Source/bindings/core/v8/TraceWrapperMember.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 TraceWrapperMember_h
 #define TraceWrapperMember_h
 
 #include "bindings/core/v8/ScriptWrappableVisitor.h"
 #include "platform/heap/HeapAllocator.h"
 
@@ skipping 19 matching lines @@
 #endif
     ScriptWrappableVisitor::writeBarrier(m_parent, raw);
   }
   TraceWrapperMember(WTF::HashTableDeletedValueType x)
       : Member<T>(x), m_parent(nullptr) {}
 
   /**
    * Copying a TraceWrapperMember means that its backpointer will also be
    * copied.
    */
   TraceWrapperMember(const TraceWrapperMember& other) { *this = other; }

[Michael Lippautz, 2016/12/09 14:46:55]

The copy ctor did not forward to the explicitly defined operator=, but to some
compiler-generated one . This is because the signatures didn't match.

 
-  template <typename U>

[Michael Lippautz, 2016/12/09 14:46:55]

There's no sense in a different type U here.

-  TraceWrapperMember& operator=(const TraceWrapperMember<U>& other) {
+  TraceWrapperMember& operator=(const TraceWrapperMember& other) {
     DCHECK(other.m_parent);
     m_parent = other.m_parent;
     Member<T>::operator=(other);
     ScriptWrappableVisitor::writeBarrier(m_parent, other);
     return *this;
   }
 
-  template <typename U>
-  TraceWrapperMember& operator=(const Member<U>& other) {
+  TraceWrapperMember& operator=(const Member<T>& other) {
     DCHECK(!traceWrapperMemberIsNotInitialized());
     Member<T>::operator=(other);
     ScriptWrappableVisitor::writeBarrier(m_parent, other);
     return *this;
   }
 
-  template <typename U>
-  TraceWrapperMember& operator=(U* other) {
+  TraceWrapperMember& operator=(T* other) {
     DCHECK(!traceWrapperMemberIsNotInitialized());
     Member<T>::operator=(other);
     ScriptWrappableVisitor::writeBarrier(m_parent, other);
     return *this;
   }
 
   TraceWrapperMember& operator=(std::nullptr_t) {
     // No need for a write barrier when assigning nullptr.
     Member<T>::operator=(nullptr);
     return *this;
@@ skipping 60 matching lines @@
   b.clear();
   b.reserveCapacity(temp.size());
   for (auto item : temp) {
     b.push_back(item.get());
   }
 }
 
 }  // namespace blink
 
 #endif  // TraceWrapperMember_h