Convert --{enable,disable}-simplified-fullscreen-ui to a feature flag.

chrome/common/chrome_switches.h

 // Copyright (c) 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.
 
 // Defines the shared command-line switches used by code in the Chrome
 // directory that don't have anywhere more specific to go.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 
@@ skipping 130 matching lines @@
 extern const char kEnablePowerOverlay[];
 extern const char kEnablePrintPreviewRegisterPromos[];
 extern const char kEnableProfiling[];
 extern const char kEnablePushApiBackgroundMode[];
 extern const char kEnableQuic[];
 extern const char kEnableQuicPortSelection[];
 extern const char kEnableAlternativeServices[];
 extern const char kEnableSessionCrashedBubble[];
 extern const char kEnableSettingsWindow[];
 extern const char kDisableSettingsWindow[];
-extern const char kEnableSimplifiedFullscreenUI[];
-extern const char kDisableSimplifiedFullscreenUI[];
 extern const char kEnableSiteEngagementAppBanner[];
 extern const char kEnableSiteEngagementEvictionPolicy[];
 extern const char kEnableSiteEngagementService[];
 extern const char kEnableSupervisedUserManagedBookmarksFolder[];
 extern const char kEnableTabAudioMuting[];
 extern const char kEnableThumbnailRetargeting[];
 extern const char kEnableUserAlternateProtocolPorts[];
 extern const char kEnableWebAppFrame[];
 extern const char kEnableWebNotificationCustomLayouts[];
 extern const char kExtensionContentVerificationBootstrap[];
@@ skipping 249 matching lines @@
 #if defined(ENABLE_TASK_MANAGER)
 bool NewTaskManagerEnabled();
 #endif  // defined(ENABLE_TASK_MANAGER)
 
 // DON'T ADD RANDOM STUFF HERE. Put it in the main section above in
 // alphabetical order, or in one of the ifdefs (also in order in each section).
 
 }  // namespace switches
 
 #endif  // CHROME_COMMON_CHROME_SWITCHES_H_