Add an about:flag for enabling a reader mode toolbar icon.

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 all the command-line switches used by Chrome.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 
 #include "build/build_config.h"
@@ skipping 141 matching lines @@
 extern const char kEnablePluginPlaceholderShadowDom[];
 extern const char kEnablePrintPreviewRegisterPromos[];
 extern const char kEnablePrivetStorage[];
 extern const char kEnableProfiling[];
 extern const char kEnableProminentURLAppFlow[];
 extern const char kEnableQueryExtraction[];
 extern const char kEnableQuic[];
 extern const char kEnableQuicPacing[];
 extern const char kEnableQuicPortSelection[];
 extern const char kEnableQuicTimeBasedLossDetection[];
+extern const char kEnableReaderModeToolbarIcon[];
 extern const char kEnableResourceContentSettings[];
 extern const char kEnableSavePasswordBubble[];
 extern const char kEnableSdchOverHttps[];
 extern const char kEnableSearchButtonInOmniboxAlways[];
 extern const char kEnableSearchButtonInOmniboxForStr[];
 extern const char kEnableSearchButtonInOmniboxForStrOrIip[];
 extern const char kEnableSessionCrashedBubble[];
 extern const char kEnableSettingsWindow[];
 extern const char kEnableShowModalDialog[];
 extern const char kDisableSettingsWindow[];
@@ skipping 226 matching lines @@
 
 bool AboutInSettingsEnabled();
 bool SettingsWindowEnabled();
 
 // 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_