Consolidate the update_client serialization code.

components/update_client/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("//net/features.gni")
 
 static_library("update_client") {
   sources = [
     "background_downloader_win.cc",
     "background_downloader_win.h",
     "component.cc",
     "component.h",
     "component_patcher.cc",
     "component_patcher.h",
     "component_patcher_operation.cc",
     "component_patcher_operation.h",
     "component_unpacker.cc",
     "component_unpacker.h",
     "configurator.h",
     "crx_downloader.cc",
     "crx_downloader.h",
     "crx_update_item.h",
     "out_of_process_patcher.h",
     "persisted_data.cc",
     "persisted_data.h",
     "ping_manager.cc",
     "ping_manager.h",
+    "protocol_builder.cc",
+    "protocol_builder.h",
     "protocol_parser.cc",
     "protocol_parser.h",
     "request_sender.cc",
     "request_sender.h",
     "task.h",
     "task_send_uninstall_ping.cc",
     "task_send_uninstall_ping.h",
     "task_update.cc",
     "task_update.h",
     "update_checker.cc",
@@ skipping 85 matching lines @@
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "component_patcher_unittest.cc",
     "component_patcher_unittest.h",
     "component_unpacker_unittest.cc",
     "persisted_data_unittest.cc",
     "ping_manager_unittest.cc",
+    "protocol_builder_unittest.cc",
     "protocol_parser_unittest.cc",
     "request_sender_unittest.cc",
     "update_checker_unittest.cc",
     "update_client_unittest.cc",
     "update_query_params_unittest.cc",
     "updater_state_unittest.cc",
     "utils_unittest.cc",
   ]
 
   if (!disable_file_support) {
     sources += [ "crx_downloader_unittest.cc" ]
   }
 
   deps = [
     ":test_support",
     ":unit_tests_bundle_data",
     ":update_client",
     "//base",
     "//components/prefs",
     "//components/prefs:test_support",
     "//components/version_info:version_info",
     "//courgette:courgette_lib",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/libxml",
   ]
 }