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

chrome/browser/ui/search/search_delegate.cc

Index: chrome/browser/ui/search/search_delegate.cc
diff --git a/chrome/browser/ui/search/search_delegate.cc b/chrome/browser/ui/search/search_delegate.cc
index 6e437c0032f8198e338a1131ee45578cbe928355..32c475227ced903538a91f77df49e5fa565347c8 100644
--- a/chrome/browser/ui/search/search_delegate.cc
+++ b/chrome/browser/ui/search/search_delegate.cc
@@ -24,12 +24,17 @@ 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);
 }