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

chrome/browser/ui/search/search_delegate.cc

 // 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.
 
 #include "chrome/browser/ui/search/search_delegate.h"
 
 #include "chrome/browser/ui/search/search_model.h"
 #include "chrome/browser/ui/search/search_tab_helper.h"
 
 namespace chrome {
 namespace search {
 
 SearchDelegate::SearchDelegate(SearchModel* browser_search_model,
                                ToolbarModel* toolbar_model)
     : browser_model_(browser_search_model),
       tab_model_() {
 }
 
 SearchDelegate::~SearchDelegate() {
   DCHECK(!tab_model_) << "All tabs should have been deactivated or closed.";
 }
 
 void SearchDelegate::ModeChanged(const Mode& old_mode, const Mode& new_mode) {
   browser_model_->SetMode(new_mode);
 }
 
+void SearchDelegate::TopBarsVisibilityChanged(const Mode& mode, bool visible) {
+  browser_model_->SetTopBarsVisible(visible);
+}
+
 void SearchDelegate::OnTabActivated(content::WebContents* web_contents) {
   if (tab_model_)
     tab_model_->RemoveObserver(this);
   tab_model_ =
       chrome::search::SearchTabHelper::FromWebContents(web_contents)->model();
   browser_model_->SetMode(tab_model_->mode());
+  browser_model_->SetTopBarsVisible(tab_model_->show_top_bars());
   tab_model_->AddObserver(this);
 }
 
 void SearchDelegate::OnTabDeactivated(content::WebContents* web_contents) {
   StopObservingTab(web_contents);
 }
 
 void SearchDelegate::OnTabDetached(content::WebContents* web_contents) {
   StopObservingTab(web_contents);
 }
 
 void SearchDelegate::StopObservingTab(content::WebContents* web_contents) {
   chrome::search::SearchTabHelper* search_tab_helper =
       chrome::search::SearchTabHelper::FromWebContents(web_contents);
   if (search_tab_helper->model() == tab_model_) {
     tab_model_->RemoveObserver(this);
     tab_model_ = NULL;
   }
 }
 
 }  // namespace search
 }  // namespace chrome