[bindings] Refactor ScriptStateForTesting, V8TestingScope into V8BindingForTesting.h/cpp

Source/bindings/core/v8/V8TestingScope.h

-// Copyright (c) 2015 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 V8TestingScope_h
-#define V8TestingScope_h
-
-#include "bindings/core/v8/ScriptState.h"
-
-#include <v8.h>
-
-namespace blink {
-
-class V8TestingScope {
-public:
-    explicit V8TestingScope(v8::Isolate*);
-    ScriptState* scriptState() const;
-    v8::Isolate* isolate() const;
-    ~V8TestingScope();
-
-private:
-    v8::HandleScope m_handleScope;
-    v8::Context::Scope m_contextScope;
-    RefPtr<ScriptState> m_scriptState;
-};
-
-} // namespace blink
-
-#endif // V8TestingScope_h