Standardize usage of virtual/override/final in cc/

BUG=417463
[email protected]

Review URL: https://codereview.chromium.org/645853008

Cr-Commit-Position: refs/heads/master@{#300439}
diff --git a/cc/test/pixel_test.h b/cc/test/pixel_test.h
index 3396099b..838acaf 100644
--- a/cc/test/pixel_test.h
+++ b/cc/test/pixel_test.h
@@ -64,7 +64,7 @@
   void EnableExternalStencilTest();
 
   // RendererClient implementation.
-  virtual void SetFullRootLayerDamage() override {}
+  void SetFullRootLayerDamage() override {}
 
  private:
   void ReadbackResult(base::Closure quit_run_loop,