Fix crash in AppNotifyChannelSetup when incognito profiles are used.

chrome/common/extensions/extension_constants.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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_
 #pragma once
 
 #include <string>
 
@@ skipping 202 matching lines @@
     INSTALL_CAUSE_AUTOMATION,
     NUM_INSTALL_CAUSES
   };
 
   enum UnloadedExtensionReason {
     UNLOAD_REASON_DISABLE,    // Extension is being disabled.
     UNLOAD_REASON_UPDATE,     // Extension is being updated to a newer version.
     UNLOAD_REASON_UNINSTALL,  // Extension is being uninstalled.
     UNLOAD_REASON_TERMINATE,  // Extension has terminated.
   };
+
+  // Error indicating that the app notifications API is not accessible by split
+  // mode extensions in incognito windows.
+  extern const char kAppNotificationsIncognitoError[];
 }  // extension_misc
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_