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

chrome/browser/ui/browser_instant_controller.cc

 // 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.
 
 #include "chrome/browser/ui/browser_instant_controller.h"
 
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_web_ui.h"
 #include "chrome/browser/instant/search.h"
@@ skipping 218 matching lines @@
   bool instant_pref_enabled = chrome::search::IsInstantPrefEnabled(profile());
   bool use_local_overlay_only = profile()->IsOffTheRecord() ||
       (!instant_pref_enabled &&
        !profile()->GetPrefs()->GetBoolean(prefs::kSearchSuggestEnabled));
   instant_.SetInstantEnabled(instant_pref_enabled, use_local_overlay_only);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // BrowserInstantController, search::SearchModelObserver implementation:
 
-void BrowserInstantController::ModeChanged(const search::Mode& old_mode,
-                                           const search::Mode& new_mode) {
+void BrowserInstantController::ModelChanged(const search::Mode& old_mode,
+                                            const search::Mode& new_mode,
+                                            bool top_bars_visible) {
+  if (old_mode == new_mode)
+    return;
+  
   if (search::IsInstantExtendedAPIEnabled()) {
     // Record some actions corresponding to the mode change. Note that to get
     // the full story, it's necessary to look at other UMA actions as well,
     // such as tab switches.
     if (new_mode.is_search_results())
       content::RecordAction(UserMetricsAction("InstantExtended.ShowSRP"));
     else if (new_mode.is_ntp())
       content::RecordAction(UserMetricsAction("InstantExtended.ShowNTP"));
   }
 
@@ skipping 85 matching lines @@
     initialized_theme_info_ = true;
   }
 
   DCHECK(initialized_theme_info_);
 
   if (browser_->search_model()->mode().is_ntp())
     instant_.ThemeChanged(theme_info_);
 }
 
 }  // namespace chrome