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

chrome/browser/ui/search/search_delegate.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_SEARCH_SEARCH_DELEGATE_H_
 #define CHROME_BROWSER_UI_SEARCH_SEARCH_DELEGATE_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "chrome/browser/ui/search/search_model_observer.h"
@@ skipping 15 matching lines @@
 // observers.
 // Changes are propagated from the active tab's model via this class to the
 // Browser-level model.
 class SearchDelegate : public SearchModelObserver {
  public:
   SearchDelegate(SearchModel* browser_search_model,
                  ToolbarModel* toolbar_model);
   virtual ~SearchDelegate();
 
   // Overrides for SearchModelObserver:
-  virtual void ModeChanged(const Mode& old_mode, const Mode& new_mode) OVERRIDE;
+  virtual void ModelChanged(const SearchModel::State& old_state,
+                            const SearchModel::State& new_state) OVERRIDE;
 
   // When the active tab is changed, the model state of this new active tab is
   // propagated to the browser.
   void OnTabActivated(content::WebContents* web_contents);
 
   // When a tab is deactivated, this class no longer observes changes to the
   // tab's model.
   void OnTabDeactivated(content::WebContents* web_contents);
 
   // When a tab is detached, this class no longer observes changes to the
@@ skipping 12 matching lines @@
   // tab.  Changes to this model are propagated through to the |browser_model_|.
   SearchModel* tab_model_;
 
   DISALLOW_COPY_AND_ASSIGN(SearchDelegate);
 };
 
 }  // namespace search
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_SEARCH_SEARCH_DELEGATE_H_