Split ExtensionMessageFilter up into a UI thread part and an IO thread part.

extensions/extensions.gyp

 # Copyright 2013 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 771 matching lines @@
         'browser/image_loader.cc',
         'browser/image_loader.h',
         'browser/image_loader_factory.cc',
         'browser/image_loader_factory.h',
         'browser/info_map.cc',
         'browser/info_map.h',
         'browser/install/crx_installer_error.h',
         'browser/install/extension_install_ui.cc',
         'browser/install/extension_install_ui.h',
         'browser/install_flag.h',
+        'browser/io_thread_extension_message_filter.cc',
+        'browser/io_thread_extension_message_filter.h',
         'browser/file_highlighter.cc',
         'browser/file_highlighter.h',
         'browser/file_reader.cc',
         'browser/file_reader.h',
         'browser/lazy_background_task_queue.cc',
         'browser/lazy_background_task_queue.h',
         'browser/management_policy.cc',
         'browser/management_policy.h',
         'browser/mojo/keep_alive_impl.cc',
         'browser/mojo/keep_alive_impl.h',
@@ skipping 455 matching lines @@
               '<(SHARED_INTERMEDIATE_DIR)/blink/devtools_resources.pak',
             ],
             'pak_output': '<(PRODUCT_DIR)/extensions_shell_and_test.pak',
           },
           'includes': [ '../build/repack_action.gypi' ],
         },
       ],
     },
   ]
 }