[bindings] Migrate V8TestingScope out of V8Binding.h/cpp

Source/bindings/core/v8/SerializedScriptValueTest.cpp

 // Copyright 2014 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.
 
 #include "config.h"
 #include "bindings/core/v8/SerializedScriptValue.h"
 
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "bindings/core/v8/SerializedScriptValueFactory.h"
 #include "bindings/core/v8/V8Binding.h"
 #include "bindings/core/v8/V8File.h"
+#include "bindings/core/v8/V8TestingScope.h"
 #include "core/fileapi/File.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebUnitTestSupport.h"
 #include <gtest/gtest.h>
 
 namespace blink {
 
 class SerializedScriptValueTest : public ::testing::Test {
 public:
     SerializedScriptValueTest()
@@ skipping 43 matching lines @@
     v8::Handle<v8::Value> v8File = serializedScriptValue->deserialize(isolate());
 
     ASSERT_TRUE(V8File::hasInstance(v8File, isolate()));
     File* file = V8File::toImpl(v8::Handle<v8::Object>::Cast(v8File));
     EXPECT_FALSE(file->hasBackingFile());
     EXPECT_EQ(File::IsNotUserVisible, file->userVisibility());
     EXPECT_EQ("hello.txt", file->name());
 }
 
 } // namespace blink