[Sync] Reimplement proto value conversions on top of field visitors.

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 435 matching lines @@
     "model_impl/model_type_store_impl.cc",
     "model_impl/model_type_store_impl.h",
     "model_impl/processor_entity_tracker.cc",
     "model_impl/processor_entity_tracker.h",
     "model_impl/shared_model_type_processor.cc",
     "model_impl/shared_model_type_processor.h",
     "protocol/proto_enum_conversions.cc",
     "protocol/proto_enum_conversions.h",
     "protocol/proto_value_conversions.cc",
     "protocol/proto_value_conversions.h",
+    "protocol/proto_visitors.h",
     "protocol/sync_protocol_error.cc",
     "protocol/sync_protocol_error.h",
     "syncable/base_node.cc",
     "syncable/base_node.h",
     "syncable/base_transaction.cc",
     "syncable/base_transaction.h",
     "syncable/change_record.cc",
     "syncable/change_record.h",
     "syncable/change_reorder_buffer.cc",
     "syncable/change_reorder_buffer.h",
@@ skipping 628 matching lines @@
     deps = [
       ":fake_server_jni",
       ":sync",
       ":test_support_fake_server",
       "//base",
       "//testing/gtest",
       "//url:url",
     ]
   }
 }