Update sync API to support attachments.

sync/sync_api.gypi

 # Copyright 2013 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.
 
 {
   'include_dirs': [
     '..',
   ],
   'defines': [
     'SYNC_IMPLEMENTATION',
   ],
   'dependencies': [
     '../base/base.gyp:base',
+    '../base/base.gyp:test_support_base',
   ],
   'sources': [
     'api/attachments/attachment.cc',
     'api/attachments/attachment.h',
+    'api/attachments/attachment_service.cc',
+    'api/attachments/attachment_service.h',
     'api/attachments/attachment_store.cc',
     'api/attachments/attachment_store.h',
+    'api/attachments/fake_attachment_service.cc',
+    'api/attachments/fake_attachment_service.h',
     'api/attachments/fake_attachment_store.cc',
     'api/attachments/fake_attachment_store.h',
     'api/string_ordinal.h',
     'api/syncable_service.cc',
     'api/syncable_service.h',
     'api/sync_data.cc',
     'api/sync_data.h',
     'api/sync_change.cc',
     'api/sync_change.h',
     'api/sync_change_processor.cc',
     'api/sync_change_processor.h',
     'api/sync_error.cc',
     'api/sync_error.h',
     'api/sync_error_factory.cc',
     'api/sync_error_factory.h',
     'api/sync_merge_result.cc',
     'api/sync_merge_result.h',
     'api/time.h',
   ],
 }