ServiceWorker: Make a way to retrieve a service worker version id (Blink)

public/web/WebFrameClient.h

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 554 matching lines @@
 
     // Notifies embedder about an accessibility event.
     virtual void postAccessibilityEvent(const WebAXObject&, WebAXEvent) { }
 
     // ServiceWorker -------------------------------------------------------
 
     // Whether the document associated with WebDataSource is controlled by the
     // ServiceWorker.
     virtual bool isControlledByServiceWorker(WebDataSource&) { return false; }
 
+    // Returns an identifier of the service worker controlling the document
+    // associated with the WebDataSource.
+    virtual int64_t serviceWorkerID(WebDataSource&) { return -1; }
+
 protected:
     virtual ~WebFrameClient() { }
 };
 
 } // namespace blink
 
 #endif