Implement chrome.systemPrivate.getIncognitoModeAvailability extension API function

chrome/browser/extensions/extension_preference_api_constants.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/extensions/extension_preference_api_constants.h"
 
 namespace extension_preference_api_constants {
 
 const char kIncognitoKey[] = "incognito";
 
 const char kScopeKey[] = "scope";
 
 const char kIncognitoErrorMessage[] =
     "You do not have permission to access incognito preferences.";
 
 const char kIncognitoSessionOnlyErrorMessage[] =
     "You cannot set a preference with scope 'incognito_session_only' when no "
     "incognito window is open.";
 
 const char kPermissionErrorMessage[] =
     "You do not have permission to access the preference '*'. "
     "Be sure to declare in your manifest what permissions you need.";
 
+const char kCannotModifyReadOnlyMessage[] =
+    "You cannot modify the read-only preference '*'.";
+
 }  // extension_preference_api_constants