Remove extension-to-component migration mechanism

chrome/test/BUILD.gn

 # 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 3894 matching lines @@
       "../browser/extensions/api/web_request/web_request_event_details_unittest.cc",
       "../browser/extensions/api/web_request/web_request_permissions_unittest.cc",
       "../browser/extensions/app_data_migrator_unittest.cc",
       "../browser/extensions/blacklist_state_fetcher_unittest.cc",
       "../browser/extensions/bookmark_app_helper_unittest.cc",
       "../browser/extensions/chrome_app_sorting_unittest.cc",
       "../browser/extensions/chrome_component_extension_resource_manager_unittest.cc",
       "../browser/extensions/chrome_extension_function_unittest.cc",
       "../browser/extensions/chrome_info_map_unittest.cc",
       "../browser/extensions/component_loader_unittest.cc",
-      "../browser/extensions/component_migration_helper_unittest.cc",
       "../browser/extensions/convert_user_script_unittest.cc",
       "../browser/extensions/convert_web_app_unittest.cc",
       "../browser/extensions/default_apps_unittest.cc",
       "../browser/extensions/display_info_provider_chromeos_unittest.cc",
       "../browser/extensions/error_console/error_console_unittest.cc",
       "../browser/extensions/event_router_forwarder_unittest.cc",
       "../browser/extensions/extension_action_icon_factory_unittest.cc",
       "../browser/extensions/extension_action_manager_unittest.cc",
       "../browser/extensions/extension_action_runner_unittest.cc",
       "../browser/extensions/extension_action_unittest.cc",
@@ skipping 1225 matching lines @@
 }
 
 if (is_win) {
   loadable_module("conflicts_dll") {
     testonly = true
     sources = [
       "conflicts/conflicts_dll.cc",
     ]
   }
 }