Add about:flags entry for Mac V2 sandbox.

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 1190 matching lines @@
 
 extern const char kHostedAppsInWindowsName[];
 extern const char kHostedAppsInWindowsDescription[];
 
 extern const char kMacRTLName[];
 extern const char kMacRTLDescription[];
 
 extern const char kMacTouchBarName[];
 extern const char kMacTouchBarDescription[];
 
+extern const char kMacV2SandboxName[];
+extern const char kMacV2SandboxDescription[];
+
 extern const char kMacViewsNativeAppWindowsName[];
 extern const char kMacViewsNativeAppWindowsDescription[];
 
 extern const char kMacViewsTaskManagerName[];
 extern const char kMacViewsTaskManagerDescription[];
 
 extern const char kTabDetachingInFullscreenName[];
 extern const char kTabDetachingInFullscreenDescription[];
 
 extern const char kTabStripKeyboardFocusName[];
@@ skipping 307 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_