Added flag in chrome://flags to enable the New Launcher UI.

ui/app_list/app_list_switches.h

 // Copyright 2013 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.
 
 #ifndef UI_APP_LIST_APP_LIST_SWITCHES_H_
 #define UI_APP_LIST_APP_LIST_SWITCHES_H_
 
 #include "build/build_config.h"
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 namespace switches {
 
 // Please keep these flags sorted (but keep enable/disable pairs together).
 APP_LIST_EXPORT extern const char kCustomLauncherPage[];
 APP_LIST_EXPORT extern const char kDisableAppListDismissOnBlur[];
 APP_LIST_EXPORT extern const char kEnableAppList[];
+APP_LIST_EXPORT extern const char kEnableFullscreenAppList[];
 APP_LIST_EXPORT extern const char kEnableSyncAppList[];
 APP_LIST_EXPORT extern const char kDisableSyncAppList[];
 APP_LIST_EXPORT extern const char kEnableDriveSearchInChromeLauncher[];
 APP_LIST_EXPORT extern const char kDisableDriveSearchInChromeLauncher[];
 APP_LIST_EXPORT extern const char kResetAppListInstallState[];
 
 bool APP_LIST_EXPORT IsAppListSyncEnabled();
 
+bool APP_LIST_EXPORT IsFullscreenAppListEnabled();
+
 bool APP_LIST_EXPORT IsFolderUIEnabled();
 
 bool APP_LIST_EXPORT IsVoiceSearchEnabled();
 
 // Determines whether the app list should not be dismissed on focus loss.
 bool APP_LIST_EXPORT ShouldNotDismissOnBlur();
 
 bool APP_LIST_EXPORT IsDriveAppsInAppListEnabled();
 
 bool APP_LIST_EXPORT IsDriveSearchInChromeLauncherEnabled();
 
 }  // namespace switches
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_SWITCHES_H_