ServiceWorker: register() should return the existing registration object if available

Source/platform/exported/WebServiceWorkerRegistrationProxy.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 "public/platform/WebServiceWorkerRegistrationProxy.h"
+
+namespace blink {
+
+WebServiceWorkerRegistrationProxy::WebServiceWorkerRegistrationProxy(ServiceWorkerRegistration* registration)
+    : m_private(registration)
+{
+}
+
+WebServiceWorkerRegistrationProxy::operator ServiceWorkerRegistration*() const
+{
+    return m_private;
+}
+
+} // namespace blink