alternate ntp: implement Show/HideBars API to reduce jank when showing/hiding bars

chrome/browser/ui/browser.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_BROWSER_H_
 #define CHROME_BROWSER_UI_BROWSER_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 664 matching lines @@
       void* params) OVERRIDE;
 
   // Overridden from content::NotificationObserver:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // Overridden from chrome::search::SearchModelObserver:
   virtual void ModeChanged(const chrome::search::Mode& old_mode,
                            const chrome::search::Mode& new_mode) OVERRIDE;
+  virtual void TopBarsVisibilityChanged(const chrome::search::Mode& mode,
+                                        bool visible) OVERRIDE;
 
   // Command and state updating ///////////////////////////////////////////////
 
   // Handle changes to kDevTools preference.
   void OnDevToolsDisabledChanged();
 
   // Set the preference that indicates that the home page has been changed.
   void MarkHomePageAsChanged();
 
   // UI update coalescing and handling ////////////////////////////////////////
@@ skipping 230 matching lines @@
   bool window_has_shown_;
 
   // Currently open color chooser. Non-NULL after OpenColorChooser is called and
   // before DidEndColorChooser is called.
   scoped_ptr<content::ColorChooser> color_chooser_;
 
   DISALLOW_COPY_AND_ASSIGN(Browser);
 };
 
 #endif  // CHROME_BROWSER_UI_BROWSER_H_