Add missing virtual keyword for methods with OVERRIDE

Source/platform/graphics/test/MockDiscardablePixelRef.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 31 matching lines @@
     ~MockDiscardablePixelRef() { }
 
     void discard()
     {
         ASSERT(!m_lockedMemory);
         discarded = true;
     }
 
     class Allocator : public SkBitmap::Allocator {
     public:
-        bool allocPixelRef(SkBitmap* dst, SkColorTable* ct) SK_OVERRIDE {
+        virtual bool allocPixelRef(SkBitmap* dst, SkColorTable* ct) SK_OVERRIDE {
             SkImageInfo info;
             if (!dst->asImageInfo(&info)) {
                 return false;
             }
             SkAutoTUnref<SkPixelRef> pr(new MockDiscardablePixelRef(info));
             dst->setPixelRef(pr);
             return true;
         }
     };
 
@@ skipping 15 matching lines @@
     }
 
 private:
     void* m_lockedMemory;
     bool discarded;
 };
 
 } // namespace WebCore
 
 #endif // MockDiscardablePixelRef_h