ServiceWorker: Implement navigate() method in WindowClient (blink side).

Source/modules/serviceworkers/ServiceWorkerWindowClient.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 ServiceWorkerWindowClient_h
 #define ServiceWorkerWindowClient_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "modules/ModulesExport.h"
 #include "modules/serviceworkers/ServiceWorkerClient.h"
@@ skipping 14 matching lines @@
 
     static ServiceWorkerWindowClient* take(ScriptPromiseResolver*, PassOwnPtr<WebType>);
 
     static ServiceWorkerWindowClient* create(const WebServiceWorkerClientInfo&);
     ~ServiceWorkerWindowClient() override;
 
     // WindowClient.idl
     String visibilityState() const;
     bool focused() const { return m_isFocused; }
     ScriptPromise focus(ScriptState*);
+    ScriptPromise navigate(ScriptState*, const String& url);
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit ServiceWorkerWindowClient(const WebServiceWorkerClientInfo&);
 
     WebPageVisibilityState m_pageVisibilityState;
     bool m_isFocused;
 };
 
 } // namespace blink
 
 #endif // ServiceWorkerWindowClient_h