Speculative fix for instant overlay crash

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"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
 
 class Browser;
 @class BrowserWindowController;
 @class OverlayableContentsController;
 
-class InstantOverlayControllerMac : public InstantOverlayController {
+class InstantOverlayControllerMac : public InstantOverlayController,
+                                    public content::NotificationObserver {
  public:
   InstantOverlayControllerMac(Browser* browser,
                               BrowserWindowController* window,
                               OverlayableContentsController* overlay);
   virtual ~InstantOverlayControllerMac();
 
  private:
-  // Overridden from InstantOverlayController:
+  // InstantOverlayController:
   virtual void OverlayStateChanged(const InstantOverlayModel& model) OVERRIDE;
 
+  // content::NotificationObserver:
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
+
   BrowserWindowController* const window_;
   OverlayableContentsController* const overlay_;
+  content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(InstantOverlayControllerMac);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_TAB_CONTENTS_INSTANT_OVERLAY_CONTROLLER_MAC_H_