Update {virtual,override} to follow C++11 style in chrome.

chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.h

 // Copyright 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_TAB_CONTENTS_INSTANT_OVERLAY_CONTROLLER_MAC_H_
 #define CHROME_BROWSER_UI_COCOA_TAB_CONTENTS_INSTANT_OVERLAY_CONTROLLER_MAC_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "chrome/browser/ui/search/instant_overlay_controller.h"
 
 class Browser;
 @class OverlayableContentsController;
 
 class InstantOverlayControllerMac : public InstantOverlayController {
  public:
   InstantOverlayControllerMac(Browser* browser,
                               OverlayableContentsController* overlay);
-  virtual ~InstantOverlayControllerMac();
+  ~InstantOverlayControllerMac() override;
 
  private:
   // Overridden from InstantOverlayController:
-  virtual void OverlayStateChanged(const InstantOverlayModel& model) override;
+  void OverlayStateChanged(const InstantOverlayModel& model) override;
 
   OverlayableContentsController* const overlay_;
 
   DISALLOW_COPY_AND_ASSIGN(InstantOverlayControllerMac);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_TAB_CONTENTS_INSTANT_OVERLAY_CONTROLLER_MAC_H_