Convert zoom callbacks to use CallbackRegistry

chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller.mm

 // Copyright (c) 2011 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.
 
 #import "chrome/browser/ui/cocoa/wrench_menu/wrench_menu_controller.h"
 
 #include "base/basictypes.h"
 #include "base/mac/bundle_locations.h"
 #include "base/mac/mac_util.h"
 #include "base/strings/string16.h"
@@ skipping 48 matching lines @@
       return false;
     *out_accelerator = *accelerator;
     return true;
   }
 };
 
 class ZoomLevelObserver {
  public:
   ZoomLevelObserver(WrenchMenuController* controller,
                     content::HostZoomMap* map)
-      : callback_(base::Bind(&ZoomLevelObserver::OnZoomLevelChanged,
-                             base::Unretained(this))),
-        controller_(controller),
+      : controller_(controller),
         map_(map) {
-    map_->AddZoomLevelChangedCallback(callback_);
+    subscription_ = map_->AddZoomLevelChangedCallback(
+        base::Bind(&ZoomLevelObserver::OnZoomLevelChanged,
+                   base::Unretained(this)));
   }
 
-  ~ZoomLevelObserver() {
-    map_->RemoveZoomLevelChangedCallback(callback_);
-  }
+  ~ZoomLevelObserver() {}
 
  private:
   void OnZoomLevelChanged(const HostZoomMap::ZoomLevelChange& change) {
     WrenchMenuModel* wrenchMenuModel = [controller_ wrenchMenuModel];
     wrenchMenuModel->UpdateZoomControls();
     const string16 level =
         wrenchMenuModel->GetLabelForCommandId(IDC_ZOOM_PERCENT_DISPLAY);
     [[controller_ zoomDisplay] setTitle:SysUTF16ToNSString(level)];
   }
 
-  content::HostZoomMap::ZoomLevelChangedCallback callback_;
+  scoped_ptr<content::HostZoomMap::Subscription> subscription_;
 
   WrenchMenuController* controller_;  // Weak; owns this.
   content::HostZoomMap* map_;  // Weak.
 
   DISALLOW_COPY_AND_ASSIGN(ZoomLevelObserver);
 };
 
 }  // namespace WrenchMenuControllerInternal
 
 @implementation WrenchMenuController
@@ skipping 307 matching lines @@
     controller_ = controller;
   }
   return self;
 }
 
 - (IBAction)dispatchWrenchMenuCommand:(id)sender {
   [controller_ dispatchWrenchMenuCommand:sender];
 }
 
 @end  // @implementation WrenchMenuButtonViewController