Add missing virtual keyword for methods with OVERRIDE

Source/core/animation/CompositorAnimationsTestHelper.h

 /*
  * Copyright (C) 2012 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
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 113 matching lines @@
     };
 
 private:
     class PlatformProxy : public blink::Platform {
     public:
         PlatformProxy(WebCompositorSupportMock** compositor) : m_compositor(compositor) { }
 
         virtual void cryptographicallyRandomValues(unsigned char* buffer, size_t length) { ASSERT_NOT_REACHED(); }
     private:
         WebCompositorSupportMock** m_compositor;
-        blink::WebCompositorSupport* compositorSupport() OVERRIDE { return *m_compositor; }
+        virtual blink::WebCompositorSupport* compositorSupport() OVERRIDE { return *m_compositor; }
     };
 
     WebCompositorSupportMock* m_mockCompositor;
     PlatformProxy m_proxyPlatform;
 
 protected:
     blink::Platform* m_platform;
 
     virtual void SetUp()
     {
@@ skipping 10 matching lines @@
     void setCompositorForTesting(WebCompositorSupportMock& mock)
     {
         ASSERT(!m_mockCompositor);
         m_mockCompositor = &mock;
     }
 };
 
 }
 
 #endif