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

chrome/browser/ui/browser_instant_controller.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_BROWSER_INSTANT_CONTROLLER_H_
 #define CHROME_BROWSER_UI_BROWSER_INSTANT_CONTROLLER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 95 matching lines @@
   void SetOmniboxBounds(const gfx::Rect& bounds);
 
  private:
   // Sets the value of |instant_| based on value from profile. Invoked
   // on pref change.
   void ResetInstant(const std::string& pref_name);
 
   // Overridden from search::SearchModelObserver:
   virtual void ModeChanged(const search::Mode& old_mode,
                            const search::Mode& new_mode) OVERRIDE;
+  virtual void TopBarsVisibilityChanged(const search::Mode& mode,
+                                        bool visible) OVERRIDE {}
 
   // content::NotificationObserver implementation.
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // Helper for handling theme change.
   void OnThemeChanged(ThemeService* theme_service);
 
   // Replaces the contents at tab |index| with |new_contents| and deletes the
@@ skipping 13 matching lines @@
   PrefChangeRegistrar profile_pref_registrar_;
 
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserInstantController);
 };
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_BROWSER_INSTANT_CONTROLLER_H_