Standardize usage of virtual/override/final in extensions/

extensions/renderer/app_window_custom_bindings.cc

Index: extensions/renderer/app_window_custom_bindings.cc
diff --git a/extensions/renderer/app_window_custom_bindings.cc b/extensions/renderer/app_window_custom_bindings.cc
index d3f32561094c7f3b6f3de39cb638209999b97799..613b1f832b67580307411c50354534ccb8c1623d 100644
--- a/extensions/renderer/app_window_custom_bindings.cc
+++ b/extensions/renderer/app_window_custom_bindings.cc
@@ -32,7 +32,7 @@ class DidCreateDocumentElementObserver : public content::RenderViewObserver {
                                    Dispatcher* dispatcher)
       : content::RenderViewObserver(view), dispatcher_(dispatcher) {}
 
-  virtual void DidCreateDocumentElement(blink::WebLocalFrame* frame) override {
+  void DidCreateDocumentElement(blink::WebLocalFrame* frame) override {
     DCHECK(frame);
     DCHECK(dispatcher_);
     // Don't attempt to inject the titlebar into iframes.