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

chrome/browser/ui/search/search_tab_helper.cc

Index: chrome/browser/ui/search/search_tab_helper.cc
diff --git a/chrome/browser/ui/search/search_tab_helper.cc b/chrome/browser/ui/search/search_tab_helper.cc
index c65d13d7562942f9cfd329061ad72a47aee6bbe0..c38cef6c6968ec8f36511967c88aabee8a2bbc9d 100644
--- a/chrome/browser/ui/search/search_tab_helper.cc
+++ b/chrome/browser/ui/search/search_tab_helper.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/ui/search/search_tab_helper.h"
 
 #include "chrome/browser/instant/search.h"
+#include "chrome/common/render_messages.h"
 #include "chrome/common/url_constants.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/notification_service.h"
@@ -35,7 +36,8 @@ namespace chrome {
 namespace search {
 
 SearchTabHelper::SearchTabHelper(content::WebContents* web_contents)
-    : is_search_enabled_(chrome::search::IsInstantExtendedAPIEnabled()),
+    : WebContentsObserver(web_contents),
+      is_search_enabled_(chrome::search::IsInstantExtendedAPIEnabled()),
       user_input_in_progress_(false),
       web_contents_(web_contents) {
   if (!is_search_enabled_)
@@ -78,6 +80,18 @@ void SearchTabHelper::Observe(
   UpdateModel();
 }
 
+bool SearchTabHelper::OnMessageReceived(const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(SearchTabHelper, message)
+    IPC_MESSAGE_HANDLER(ChromeViewHostMsg_SearchBoxShowBars,
+                        OnSearchBoxShowBars)
+    IPC_MESSAGE_HANDLER(ChromeViewHostMsg_SearchBoxHideBars,
+                        OnSearchBoxHideBars)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
 void SearchTabHelper::UpdateModel() {
   Mode::Type type = Mode::MODE_DEFAULT;
   Mode::Origin origin = Mode::ORIGIN_DEFAULT;
@@ -93,5 +107,17 @@ void SearchTabHelper::UpdateModel() {
   model_.SetMode(Mode(type, origin));
 }
 
+void SearchTabHelper::OnSearchBoxShowBars(int page_id) {
+  if (web_contents()->IsActiveEntry(page_id))
+    model_.SetTopBarsVisible(true);
+}
+
+void SearchTabHelper::OnSearchBoxHideBars(int page_id) {
+  if (web_contents()->IsActiveEntry(page_id)) {
+    model_.SetTopBarsVisible(false);
+    Send(new ChromeViewMsg_SearchBoxBarsHidden(routing_id()));
+  }
+}
+
 }  // namespace search
 }  // namespace chrome