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

public/platform/WebUnitTestSupport.h

Index: public/platform/WebUnitTestSupport.h
diff --git a/public/platform/WebUnitTestSupport.h b/public/platform/WebUnitTestSupport.h
index a8609ded171e3a93bac7d792231ca8acfc881c74..dd80f1de46188811b66b43882cacf0c4ca68974e 100644
--- a/public/platform/WebUnitTestSupport.h
+++ b/public/platform/WebUnitTestSupport.h
@@ -59,7 +59,7 @@ public:
 
     // 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(); }