Mac Chromium style checker cleanup

chrome/browser/ui/cocoa/download/download_started_animation_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This file contains the Mac implementation the download animation, displayed
 // at the start of a download. The animation produces an arrow pointing
 // downwards and animates towards the bottom of the window where the new
 // download appears in the download shelf.
 
 #include "chrome/browser/download/download_started_animation.h"
@@ skipping 47 matching lines @@
     registrar_.Add(this,
                    content::NOTIFICATION_WEB_CONTENTS_VISIBILITY_CHANGED,
                    content::Source<WebContents>(web_contents_));
     registrar_.Add(this,
                    content::NOTIFICATION_WEB_CONTENTS_DESTROYED,
                    content::Source<WebContents>(web_contents_));
   }
 
   // Runs when a tab is hidden or destroyed. Let our owner know we should end
   // the animation.
-  void Observe(int type,
-               const content::NotificationSource& source,
-               const content::NotificationDetails& details) {
+  virtual void Observe(
+      int type,
+      const content::NotificationSource& source,
+      const content::NotificationDetails& details) OVERRIDE {
     if (type == content::NOTIFICATION_WEB_CONTENTS_VISIBILITY_CHANGED) {
       bool visible = *content::Details<bool>(details).ptr();
       if (visible)
         return;
     }
     // This ends up deleting us.
     [owner_ closeAnimation];
   }
 
  private:
@@ skipping 118 matching lines @@
 }
 
 @end
 
 void DownloadStartedAnimation::Show(WebContents* web_contents) {
   DCHECK(web_contents);
 
   // Will be deleted when the animation is complete.
   [DownloadStartedAnimationMac startAnimationWithWebContents:web_contents];
 }