Implement support for fallback update check urls in the component updater

components/component_updater/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.
 
 source_set("component_updater") {
   sources = [
     "background_downloader_win.cc",
     "background_downloader_win.h",
     "component_patcher.cc",
     "component_patcher.h",
@@ skipping 12 matching lines @@
     "component_updater_switches.h",
     "component_updater_utils.cc",
     "component_updater_utils.h",
     "crx_update_item.h",
     "crx_downloader.cc",
     "crx_downloader.h",
     "default_component_installer.cc",
     "default_component_installer.h",
     "pref_names.cc",
     "pref_names.h",
+    "request_sender.cc",
+    "request_sender.h",
     "update_checker.cc",
     "update_checker.h",
     "update_response.cc",
     "update_response.h",
     "url_fetcher_downloader.cc",
     "url_fetcher_downloader.h",
   ]
 
   deps = [
     "//base",
@@ skipping 25 matching lines @@
     "//testing/gmock",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "test/component_patcher_unittest.cc",
     "test/component_updater_ping_manager_unittest.cc",
     "test/crx_downloader_unittest.cc",
+    "test/request_sender_unittest.cc",
     "test/update_checker_unittest.cc",
     "test/update_response_unittest.cc",
   ]
 
   deps = [
     ":component_updater",
     ":test_support",
     "//testing/gtest",
     "//testing/gmock",
     "//third_party/libxml",
   ]
 }