Replacing the 'return 0;' statements with 'return nullptr;'

public/platform/WebServiceWorker.h

 /*
  * Copyright (C) 2013 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 34 matching lines @@
 
 class WebServiceWorker {
 public:
     virtual ~WebServiceWorker() { }
 
     // Sets ServiceWorkerProxy, with which callee can start making upcalls
     // to the ServiceWorker object via the client. This doesn't pass the
     // ownership to the callee, and the proxy's lifetime is same as that of
     // WebServiceWorker.
     virtual void setProxy(WebServiceWorkerProxy*) { }
-    virtual WebServiceWorkerProxy* proxy() { return 0; }
+    virtual WebServiceWorkerProxy* proxy() { return nullptr; }
 
     virtual WebURL url() const { return WebURL(); }
     virtual WebServiceWorkerState state() const { return WebServiceWorkerStateUnknown; }
 
     // Callee receives ownership of the passed vector.
     // FIXME: Blob refs should be passed to maintain ref counts. crbug.com/351753
     virtual void postMessage(const WebString&, WebMessagePortChannelArray*) { BLINK_ASSERT_NOT_REACHED(); }
 
     virtual void terminate() { }
 };
 
 }
 
 #endif // WebServiceWorker_h