Address some TODOs for ChooserBubbleDelegate class

chrome/browser/ui/cocoa/website_settings/chooser_bubble_ui_cocoa.h

 // Copyright 2015 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_WEBSITE_SETTINGS_CHOOSER_BUBBLE_UI_COCOA_H_
 #define CHROME_BROWSER_UI_COCOA_WEBSITE_SETTINGS_CHOOSER_BUBBLE_UI_COCOA_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/macros.h"
@@ skipping 14 matching lines @@
                        ChooserBubbleDelegate* chooser_bubble_delegate);
   ~ChooserBubbleUiCocoa() override;
 
   // BubbleUi:
   void Show(BubbleReference bubble_reference) override;
   void Close() override;
   void UpdateAnchorPosition() override;
 
   // ChooserBubbleDelegate::Observer:
   void OnOptionsInitialized() override;
-  void OnOptionAdded(int index) override;
-  void OnOptionRemoved(int index) override;
+  void OnOptionAdded(size_t index) override;
+  void OnOptionRemoved(size_t index) override;
 
   // Called when |chooser_bubble_ui_controller_| is closing.
   void OnBubbleClosing();
 
  private:
   Browser* browser_;                                // Weak.
   ChooserBubbleDelegate* chooser_bubble_delegate_;  // Weak.
   // Cocoa-side chooser bubble UI controller. Weak, as it will close itself.
   ChooserBubbleUiController* chooser_bubble_ui_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(ChooserBubbleUiCocoa);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_WEBSITE_SETTINGS_CHOOSER_BUBBLE_UI_COCOA_H_