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

chrome/browser/flag_descriptions.h

 // Copyright 2017 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 CHROME_BROWSER_FLAG_DESCRIPTIONS_H_
 #define CHROME_BROWSER_FLAG_DESCRIPTIONS_H_
 
 // Includes needed for macros allowing conditional compilation of some strings.
 #include "build/build_config.h"
 #include "build/buildflag.h"
@@ skipping 1266 matching lines @@
 
 extern const char kDisableNewVirtualKeyboardBehaviorName[];
 extern const char kDisableNewVirtualKeyboardBehaviorDescription[];
 
 extern const char kDisableSystemTimezoneAutomaticDetectionName[];
 extern const char kDisableSystemTimezoneAutomaticDetectionDescription[];
 
 extern const char kDisplayColorCalibrationName[];
 extern const char kDisplayColorCalibrationDescription[];
 
+extern const char kEnableFullscreenAppListName[];
+extern const char kEnableFullscreenAppListDescription[];
+
 extern const char kEnableAndroidWallpapersAppName[];
 extern const char kEnableAndroidWallpapersAppDescription[];
 
 extern const char kEnableChromevoxArcSupportName[];
 extern const char kEnableChromevoxArcSupportDescription[];
 
 extern const char kEnableEhvInputName[];
 extern const char kEnableEhvInputDescription[];
 
 extern const char kEnableEncryptionMigrationName[];
@@ skipping 248 matching lines @@
 #endif  // defined(TOOLKIT_VIEWS) || defined(OS_ANDROID)
 
 // ============================================================================
 // Don't just add flags to the end, put them in the right section in
 // alphabetical order. See top instructions for more.
 // ============================================================================
 
 }  // namespace flag_descriptions
 
 #endif  // CHROME_BROWSER_FLAG_DESCRIPTIONS_H_