Add blink-side binding code and tests for ServiceWorker -> Document postMessage (3/3)

Source/modules/serviceworkers/Client.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 Client_h
 #define Client_h
 
 #include "bindings/v8/ScriptWrappable.h"
+#include "bindings/v8/SerializedScriptValue.h"
 #include "wtf/Forward.h"
 
 namespace WebCore {
 
 class Client FINAL : public RefCounted<Client>, public ScriptWrappable {
 public:
     static PassRefPtr<Client> create(unsigned id);
     ~Client();
 
     // Client.idl
     unsigned id() const { return m_id; }
+    void postMessage(ExecutionContext*, PassRefPtr<SerializedScriptValue> message, const MessagePortArray*, ExceptionState&);
 
 private:
     explicit Client(unsigned id);
 
     unsigned m_id;
 };
 
 } // namespace WebCore
 
 #endif // Client_h