v8binding: Separate TraceWrapperBase.h from ScriptWrappable.h.

Creates a new header TraceWrapperBase.h and makes ScriptWrappable.h
and TraceWrapperMember.h include TraceWrapperBase.h that defines
TraceWrapperBase class.

Bug: 
Change-Id: I9135b9394ef4a116322d6f9fc1ac97969e4735f3
Reviewed-on: https://chromium-review.googlesource.com/664503Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501603}

third_party/WebKit/Source/platform/BUILD.gn

@@ -523,6 +523,7 @@ component("platform") {
     "bindings/StringResource.cpp",
     "bindings/StringResource.h",
     "bindings/ToV8.h",
+    "bindings/TraceWrapperBase.h",
     "bindings/TraceWrapperMember.h",
     "bindings/TraceWrapperV8Reference.h",
     "bindings/V0CustomElementBinding.cpp",

third_party/WebKit/Source/platform/bindings/ScriptWrappable.h

@@ -33,7 +33,7 @@
 
 #include "build/build_config.h"
 #include "platform/PlatformExport.h"
-#include "platform/bindings/ScriptWrappableVisitor.h"
+#include "platform/bindings/TraceWrapperBase.h"
 #include "platform/bindings/WrapperTypeInfo.h"
 #include "platform/heap/Handle.h"
 #include "platform/wtf/Noncopyable.h"
@@ -42,16 +42,6 @@
 
 namespace blink {
 
-class PLATFORM_EXPORT TraceWrapperBase {
-  WTF_MAKE_NONCOPYABLE(TraceWrapperBase);
-
- public:
-  TraceWrapperBase() = default;
-  virtual bool IsScriptWrappable() const { return false; }
-
-  DECLARE_VIRTUAL_TRACE_WRAPPERS(){};
-};
-
 // ScriptWrappable provides a way to map from/to C++ DOM implementation to/from
 // JavaScript object (platform object).  ToV8() converts a ScriptWrappable to
 // a v8::Object and toScriptWrappable() converts a v8::Object back to

third_party/WebKit/Source/platform/bindings/TraceWrapperBase.h

+// Copyright 2017 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 TraceWrapperBase_h
+#define TraceWrapperBase_h
+
+#include "platform/bindings/ScriptWrappableVisitor.h"
+#include "platform/wtf/Noncopyable.h"
+
+namespace blink {
+
+class PLATFORM_EXPORT TraceWrapperBase {
+  WTF_MAKE_NONCOPYABLE(TraceWrapperBase);
+
+ public:
+  TraceWrapperBase() = default;
+  ~TraceWrapperBase() = default;
+  virtual bool IsScriptWrappable() const { return false; }
+
+  DEFINE_INLINE_VIRTUAL_TRACE_WRAPPERS() {}
+};
+
+}  // namespace blink
+
+#endif  // TraceWrapperBase_h

third_party/WebKit/Source/platform/bindings/TraceWrapperMember.h

@@ -6,6 +6,7 @@
 #define TraceWrapperMember_h
 
 #include "platform/bindings/ScriptWrappableVisitor.h"
+#include "platform/bindings/TraceWrapperBase.h"
 #include "platform/heap/HeapAllocator.h"
 
 namespace blink {
@@ -20,6 +21,9 @@ class Member;
 template <class T>
 class TraceWrapperMember : public Member<T> {
   DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
+  // TODO(mlippautz): Enable the following check.
+  // static_assert(std::is_base_of<TraceWrapperBase, T>::value,
+  //               "T must inherit from TraceWrapperBase");
 
  public:
   TraceWrapperMember() : Member<T>(nullptr) {}