Add missing virtual keyword for methods with OVERRIDE

Source/core/animation/CompositorAnimationsTestHelper.h

Index: Source/core/animation/CompositorAnimationsTestHelper.h
diff --git a/Source/core/animation/CompositorAnimationsTestHelper.h b/Source/core/animation/CompositorAnimationsTestHelper.h
index 732d34662e5b4ae7704fc7fa78bb07302be1db4e..bb2761f75fc4fd16b6a67b7246714516c9cfbd7e 100644
--- a/Source/core/animation/CompositorAnimationsTestHelper.h
+++ b/Source/core/animation/CompositorAnimationsTestHelper.h
@@ -131,7 +131,7 @@ private:
         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;