Introduce WebServiceWorkerNetworkProvider::GetProviderID() and stop static casting

third_party/WebKit/public/platform/modules/serviceworker/WebServiceWorkerNetworkProvider.h

 /*
  * Copyright (C) 2014 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 37 matching lines @@
 
   // A request is about to be sent out, and the client may modify it. Request
   // is writable, and changes to the URL, for example, will change the request
   // made.
   virtual void WillSendRequest(WebURLRequest&) {}
 
   // Whether the document associated with WebDataSource is controlled by the
   // ServiceWorker.
   virtual bool IsControlledByServiceWorker() { return false; }
 
+  // Returns an identifier of this provider.
+  virtual int GetProviderID() const { return -1; }
+
   // Returns an identifier of the service worker controlling the document
   // associated with the WebDataSource.
   virtual int64_t ServiceWorkerID() { return -1; }
 };
 
 }  // namespace blink
 
 #endif  // WebServiceWorkerNetworkProvider_h