Move the Extension Port implementation out of messaging.js into its own file port.js.

extensions/extensions.gypi

 # Copyright 2015 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': {
     'extensions_common_constants_sources': [
       'common/constants.cc',
       'common/constants.h',
     ],
@@ skipping 901 matching lines @@
       'renderer/resources/greasemonkey_api.js',
       'renderer/resources/i18n_custom_bindings.js',
       'renderer/resources/image_util.js',
       'renderer/resources/json_schema.js',
       'renderer/resources/last_error.js',
       'renderer/resources/messaging.js',
       'renderer/resources/messaging_utils.js',
       'renderer/resources/permissions_custom_bindings.js',
       'renderer/resources/platform_app.css',
       'renderer/resources/platform_app.js',
+      'renderer/resources/port.js',
       'renderer/resources/runtime_custom_bindings.js',
       'renderer/resources/schema_utils.js',
       'renderer/resources/send_request.js',
       'renderer/resources/set_icon.js',
       'renderer/resources/storage_area.js',
       'renderer/resources/test_custom_bindings.js',
       'renderer/resources/uncaught_exception_handler.js',
       'renderer/resources/unload_event.js',
       'renderer/resources/utils.js',
       'renderer/resources/guest_view/extension_view/extension_view.js',
@@ skipping 98 matching lines @@
       'test/result_catcher.h',
       'test/test_content_utility_client.cc',
       'test/test_content_utility_client.h',
       'test/test_extensions_client.cc',
       'test/test_extensions_client.h',
       'test/test_permission_message_provider.cc',
       'test/test_permission_message_provider.h',
     ],
   },
 }