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

public/platform/WebUnitTestSupport.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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 41 matching lines @@
 
     // Causes all pending asynchronous requests to be served. When this method
     // returns all the pending requests have been processed.
     virtual void serveAsynchronousMockedRequests() { }
 
     // Returns the root directory of the WebKit code.
     virtual WebString webKitRootDir() { return WebString(); }
 
     // Constructs a WebLayerTreeView set up with reasonable defaults for
     // testing.
-    virtual WebLayerTreeView* createLayerTreeViewForTesting() { return 0; }
+    virtual WebLayerTreeView* createLayerTreeViewForTesting() { return nullptr; }
 
     virtual WebData readFromFile(const WebString& path) { return WebData(); }
 
     // Gets the blob items from the blob handle's uuid.
     // The ownership of WebBlobData::Items is not transferred.
     virtual bool getBlobItems(const WebString& uuid, WebVector<WebBlobData::Item*>*) { return false; }
 
     virtual void enterRunLoop() { }
     virtual void exitRunLoop() { }
 };
 
 }
 
 #endif // WebUnitTestSupport_h