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

chrome/browser/ui/cocoa/tab_contents/instant_overlay_controller_mac.mm

 // 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/cocoa/tab_contents/instant_overlay_controller_mac.h"
+
 #include "chrome/browser/instant/instant_overlay_model.h"
+#include "chrome/browser/instant/search.h"
 #include "chrome/browser/ui/browser.h"
 #import "chrome/browser/ui/cocoa/browser_window_controller.h"
 #import "chrome/browser/ui/cocoa/tab_contents/overlayable_contents_controller.h"
+#include "chrome/browser/ui/search/search_model.h"
+#include "chrome/browser/ui/search/search_tab_helper.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
 
 InstantOverlayControllerMac::InstantOverlayControllerMac(
     Browser* browser,
     BrowserWindowController* window,
     OverlayableContentsController* overlay)
     : InstantOverlayController(browser),
       window_(window),
       overlay_(overlay) {
 }
 
 InstantOverlayControllerMac::~InstantOverlayControllerMac() {
 }
 
 void InstantOverlayControllerMac::OverlayStateChanged(
     const InstantOverlayModel& model) {
+  // TODO(sail): migrate from InstantOverlayControllerViews::OverlayStateChanged
+  // to only call SetTopBarsVisible if we did something with overlay; this
+  // prevents the top bars from flashing in this transition
+  // DEFAULT->SUGGESTIONS->SERP.
+  bool has_overlay = false;
   if (model.mode().is_ntp() || model.mode().is_search_suggestions()) {
     // Drop shadow is only needed if search mode is not |NTP| and overlay does
     // not fill up the entire contents page.
     BOOL drawDropShadow = !model.mode().is_ntp() &&
         !(model.height() == 100 &&
           model.height_units() == INSTANT_SIZE_PERCENT);
     [overlay_ setOverlay:model.GetOverlayContents()
                   height:model.height()
              heightUnits:model.height_units()
           drawDropShadow:drawDropShadow];
+    has_overlay = true;
   } else {
     [overlay_ setOverlay:NULL
                   height:0
              heightUnits:INSTANT_SIZE_PIXELS
           drawDropShadow:NO];
   }
-  browser_->MaybeUpdateBookmarkBarStateForInstantOverlay(model.mode());
+
+  if (chrome::search::IsInstantExtendedAPIEnabled()) {
+    // Set top bars (bookmark and info bars) visibility for current tab via
+    // |SearchTabHelper| of current active web contents: top bars are hidden if
+    // there's overlay.
+    chrome::search::SearchTabHelper* search_tab_helper =
+        chrome::search::SearchTabHelper::FromWebContents(
+            browser_->tab_strip_model()->GetActiveWebContents());
+    if (search_tab_helper)
+      search_tab_helper->model()->SetTopBarsVisible(!has_overlay);
+  }
+
   [window_ updateBookmarkBarStateForInstantOverlay];
 }