[Sync] Start implementation of migration for USS.

components/sync/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/buildflag_header.gni")
 import("//build/config/features.gni")
 import("//components/sync/protocol/protocol_sources.gni")
 import("//testing/test.gni")
 
 static_library("sync") {
@@ skipping 361 matching lines @@
     "engine_impl/syncer_proto_util.h",
     "engine_impl/syncer_types.h",
     "engine_impl/syncer_util.cc",
     "engine_impl/syncer_util.h",
     "engine_impl/traffic_logger.cc",
     "engine_impl/traffic_logger.h",
     "engine_impl/update_applicator.cc",
     "engine_impl/update_applicator.h",
     "engine_impl/update_handler.cc",
     "engine_impl/update_handler.h",
+    "engine_impl/uss_migrator.cc",
+    "engine_impl/uss_migrator.h",
     "engine_impl/worker_entity_tracker.cc",
     "engine_impl/worker_entity_tracker.h",
     "js/js_backend.h",
     "js/js_controller.h",
     "js/js_event_details.cc",
     "js/js_event_details.h",
     "js/js_event_handler.h",
     "js/sync_js_controller.cc",
     "js/sync_js_controller.h",
     "model/attachments/attachment.cc",
@@ skipping 487 matching lines @@
     "engine_impl/js_sync_manager_observer_unittest.cc",
     "engine_impl/model_type_registry_unittest.cc",
     "engine_impl/model_type_worker_unittest.cc",
     "engine_impl/net/sync_server_connection_manager_unittest.cc",
     "engine_impl/sync_encryption_handler_impl_unittest.cc",
     "engine_impl/sync_manager_impl_unittest.cc",
     "engine_impl/sync_scheduler_impl_unittest.cc",
     "engine_impl/syncer_proto_util_unittest.cc",
     "engine_impl/syncer_unittest.cc",
     "engine_impl/syncer_util_unittest.cc",
+    "engine_impl/uss_migrator_unittest.cc",
     "engine_impl/worker_entity_tracker_unittest.cc",
     "js/js_event_details_unittest.cc",
     "js/sync_js_controller_unittest.cc",
     "model/attachments/attachment_id_unittest.cc",
     "model/attachments/attachment_metadata_unittest.cc",
     "model/attachments/attachment_service_proxy_unittest.cc",
     "model/attachments/attachment_unittest.cc",
     "model/entity_data_unittest.cc",
     "model/model_type_service_unittest.cc",
     "model/mutable_data_batch_unittest.cc",
@@ skipping 225 matching lines @@
     deps = [
       ":fake_server_jni",
       ":sync",
       ":test_support_fake_server",
       "//base",
       "//testing/gtest",
       "//url:url",
     ]
   }
 }