[ServiceWorker] Make Response class better conformance with the spec.

Source/modules/serviceworkers/HeaderMapForEachCallback.h

-// 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.
-
-#ifndef HeaderMapForEachCallback_h
-#define HeaderMapForEachCallback_h
-
-#include "bindings/core/v8/ScriptValue.h"
-
-namespace WebCore {
-
-class HeaderMap;
-
-class HeaderMapForEachCallback {
-public:
-    virtual ~HeaderMapForEachCallback() { }
-    virtual bool handleItem(ScriptValue thisValue, const String& value, const String& key, HeaderMap*) = 0;
-    virtual bool handleItem(const String& value, const String& key, HeaderMap*) = 0;
-};
-
-} // namespace WebCore
-
-#endif // HeaderMapForEachCallback_h