Standardize usage of virtual/override/final in extensions/

extensions/renderer/object_backed_native_handler.h

Index: extensions/renderer/object_backed_native_handler.h
diff --git a/extensions/renderer/object_backed_native_handler.h b/extensions/renderer/object_backed_native_handler.h
index d466c233719508f5e9cdc0a04747ce31f375a1e9..f31103fb645bf63db32544aef36f6c32179f4ccb 100644
--- a/extensions/renderer/object_backed_native_handler.h
+++ b/extensions/renderer/object_backed_native_handler.h
@@ -24,11 +24,11 @@ class ScriptContext;
 class ObjectBackedNativeHandler : public NativeHandler {
  public:
   explicit ObjectBackedNativeHandler(ScriptContext* context);
-  virtual ~ObjectBackedNativeHandler();
+  ~ObjectBackedNativeHandler() override;
 
   // Create an object with bindings to the native functions defined through
   // RouteFunction().
-  virtual v8::Handle<v8::Object> NewInstance() override;
+  v8::Handle<v8::Object> NewInstance() override;
 
   v8::Isolate* GetIsolate() const;
 
@@ -44,7 +44,7 @@ class ObjectBackedNativeHandler : public NativeHandler {
 
   ScriptContext* context() const { return context_; }
 
-  virtual void Invalidate() override;
+  void Invalidate() override;
 
  private:
   // Callback for RouteFunction which routes the V8 call to the correct