Standardize usage of virtual/override/final in mojo/

mojo/bindings/js/waiting_callback.h

Index: mojo/bindings/js/waiting_callback.h
diff --git a/mojo/bindings/js/waiting_callback.h b/mojo/bindings/js/waiting_callback.h
index 2a4374a500f1081fd11dca81f91b6dff4aac6fda..8baa8a0f05ee5ccf8c757cff92d85c4f8cf61e24 100644
--- a/mojo/bindings/js/waiting_callback.h
+++ b/mojo/bindings/js/waiting_callback.h
@@ -37,7 +37,7 @@ class WaitingCallback : public gin::Wrappable<WaitingCallback>,
   WaitingCallback(v8::Isolate* isolate,
                   v8::Handle<v8::Function> callback,
                   gin::Handle<HandleWrapper> handle_wrapper);
-  virtual ~WaitingCallback();
+  ~WaitingCallback() override;
 
   // Callback from MojoAsyncWaiter. |closure| is the WaitingCallback.
   static void CallOnHandleReady(void* closure, MojoResult result);
@@ -47,7 +47,7 @@ class WaitingCallback : public gin::Wrappable<WaitingCallback>,
 
   // Invoked by the HandleWrapper if the handle is closed while this wait is
   // still in progress.
-  virtual void OnWillCloseHandle() override;
+  void OnWillCloseHandle() override;
 
   base::WeakPtr<gin::Runner> runner_;
   MojoAsyncWaitID wait_id_;