Refactor browser window zoom handling and enable zoom icon on all platforms.

chrome/browser/ui/tab_contents/tab_contents.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_TAB_CONTENTS_TAB_CONTENTS_H_
 #define CHROME_BROWSER_UI_TAB_CONTENTS_TAB_CONTENTS_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 220 matching lines @@
   }
 
   TranslateTabHelper* translate_tab_helper() {
     return translate_tab_helper_.get();
   }
 
   WebIntentPickerController* web_intent_picker_controller() {
     return web_intent_picker_controller_.get();
   }
 
-  ZoomController* zoom_controller() {
+  ZoomController* zoom_controller() const {
     return zoom_controller_.get();
   }
 
   // Overrides -----------------------------------------------------------------
 
   // content::WebContentsObserver overrides:
   virtual void WebContentsDestroyed(content::WebContents* tab) OVERRIDE;
 
  private:
   // Used to retrieve this object from |web_contents_|, which is placed in
@@ skipping 77 matching lines @@
 
   // The supporting objects need to outlive the WebContents dtor (as they may
   // be called upon during its execution). As a result, this must come last
   // in the list.
   scoped_ptr<content::WebContents> web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(TabContents);
 };
 
 #endif  // CHROME_BROWSER_UI_TAB_CONTENTS_TAB_CONTENTS_H_