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

chrome/browser/instant/search.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/instant/search.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "chrome/browser/instant/instant_service.h"
 #include "chrome/browser/instant/instant_service_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search_engines/template_url_service.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
+#include "chrome/common/search_types.h"
 #include "chrome/common/url_constants.h"
 #include "components/user_prefs/pref_registry_syncable.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/web_contents.h"
 
 namespace chrome {
 namespace search {
 
 namespace {
@@ skipping 485 matching lines @@
   const std::string search_path = search_url.path();
 
   GURL::Replacements replacements;
   replacements.SetSchemeStr(search_scheme);
   replacements.SetHostStr(search_host);
   replacements.SetPortStr(search_port);
   replacements.SetPathStr(search_path);
   return instant_url.ReplaceComponents(replacements);
 }
 
+bool ShouldHandleTopBarsVisibilityChange(const Mode& old_mode,
+                                         const Mode& new_mode) {
+  // If mode has changed, only handle top bars visibility change if new mode
+  // is not |SEARCH_SUGGESTIONS| or |SEARCH_RESULTS|.  Top bars visibility for
+  // these 2 modes is determined when the mode stays the same, and:
+  // - for |NTP/SERP| pages: by SearchBox API, or
+  // - for |DEFAULT| pages: by platform-specific implementation of
+  //   |InstantOverlayController| when it shows/hides the Instant overlay.
+  return old_mode != new_mode ? !new_mode.is_search() : new_mode.is_search();
+}
+
 }  // namespace search
 }  // namespace chrome