Cleanup: Prevent usage of various extension headers when extensions support is not compiled in.

extensions/browser/notification_types.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_NOTIFICATION_TYPES_H_
 #define EXTENSIONS_BROWSER_NOTIFICATION_TYPES_H_
 
 #include "content/public/browser/notification_types.h"
 
+#if !defined(ENABLE_EXTENSIONS)
+#error "Extensions must be enabled"
+#endif
+
 namespace extensions {
 
 // Only notifications fired by the extensions module should be here. The
 // extensions module should not listen to notifications fired by the
 // embedder.
 enum NotificationType {
+  // WARNING: Do not change this.

[Yoyo Zhou, 2014/10/16 22:18:52]

This is unnecessarily ominous. Why not point to the file that depends on it?

[Lei Zhang, 2014/10/17 02:05:56]

Sure. Done.

   NOTIFICATION_EXTENSIONS_START = content::NOTIFICATION_CONTENT_END,
 
   // Sent when a CrxInstaller finishes. Source is the CrxInstaller that
   // finished. The details are the extension which was installed.
   NOTIFICATION_CRX_INSTALLER_DONE = NOTIFICATION_EXTENSIONS_START,
 
   // Sent when the known installed extensions have all been loaded.  In
   // testing scenarios this can happen multiple times if extensions are
   // unloaded and reloaded. The source is a BrowserContext*.
   //
@@ skipping 177 matching lines @@
 
   // Sent when there are new user scripts available.  The details are a
   // pointer to SharedMemory containing the new scripts.
   NOTIFICATION_USER_SCRIPTS_UPDATED,
   NOTIFICATION_EXTENSIONS_END
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_NOTIFICATION_TYPES_H_