Standardize usage of virtual/override/final specifiers in cc/.

cc/test/layer_tree_test.h

Index: cc/test/layer_tree_test.h
diff --git a/cc/test/layer_tree_test.h b/cc/test/layer_tree_test.h
index 1587f2c95b70edcf726468d98eca3ac171afd00f..1bb935248e3f0c6a49e98ac84bd1fad5158c683c 100644
--- a/cc/test/layer_tree_test.h
+++ b/cc/test/layer_tree_test.h
@@ -132,7 +132,7 @@ class TimeoutTask;
 // thread, but be aware that ending the test is an asynchronous process.
 class LayerTreeTest : public testing::Test, public TestHooks {
  public:
-  virtual ~LayerTreeTest();
+  ~LayerTreeTest() override;
 
   virtual void EndTest();
   void EndTestAfterDelayMs(int delay_milliseconds);