[ServiceWorker] Implement ServiceWorkerClients.openWindow().

Source/modules/serviceworkers/ServiceWorkerClients.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 ServiceWorkerClients_h
 #define ServiceWorkerClients_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "modules/serviceworkers/ClientQueryOptions.h"
 #include "platform/heap/Handle.h"
 #include "public/platform/WebServiceWorkerClientsInfo.h"
 
 namespace blink {
 
 class ScriptPromise;
 class ScriptState;
 
 class ServiceWorkerClients final : public GarbageCollected<ServiceWorkerClients>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static ServiceWorkerClients* create();
 
     // Clients.idl
     ScriptPromise getAll(ScriptState*, const ClientQueryOptions&);
+    ScriptPromise openWindow(ScriptState*, const String& url);
     ScriptPromise claim(ScriptState*);
 
     void trace(Visitor*) { }
 
 private:
     ServiceWorkerClients();
 };
 
 } // namespace blink
 
 #endif // ServiceWorkerClients_h