Devirtualize Visitor and remove inline visitor specialization.

third_party/WebKit/Source/platform/heap/Member.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 Member_h
 #define Member_h
 
 #include "wtf/Allocator.h"
 #include "wtf/HashFunctions.h"
 #include "wtf/HashTraits.h"
@@ skipping 416 matching lines @@
   }
 
   WeakMember& operator=(std::nullptr_t) {
     this->m_raw = nullptr;
     return *this;
   }
 
  private:
   T** cell() const { return const_cast<T**>(&this->m_raw); }
 
-  template <typename Derived>
-  friend class VisitorHelper;
+  friend class Visitor;
 };
 
 // UntracedMember is a pointer to an on-heap object that is not traced for some
 // reason. Please don't use this unless you understand what you're doing.
 // Basically, all pointers to on-heap objects must be stored in either of
 // Persistent, Member or WeakMember. It is not allowed to leave raw pointers to
 // on-heap objects. However, there can be scenarios where you have to use raw
 // pointers for some reason, and in that case you can use UntracedMember. Of
 // course, it must be guaranteed that the pointing on-heap object is kept alive
 // while the raw pointer is pointing to the object.
@@ skipping 118 matching lines @@
 
 template <typename T>
 struct IsTraceable<blink::TraceWrapperMember<T>> {
   STATIC_ONLY(IsTraceable);
   static const bool value = true;
 };
 
 }  // namespace WTF
 
 #endif  // Member_h