Instantiate AttachmentDownloader and use it in AttachmentServiceImpl

sync/sync_tests.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.
 
 {
   'targets': [
     # Test support files for the 'sync_core' target.
     {
       'target_name': 'test_support_sync_core',
       'type': 'static_library',
@@ skipping 470 matching lines @@
         'sync',
         'test_support_sync_internal_api',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '..',
         ],
         'sources': [
           'api/attachments/attachment_unittest.cc',
           'api/attachments/attachment_id_unittest.cc',
+          'api/attachments/attachment_service_impl_unittest.cc',
           'api/attachments/attachment_service_proxy_unittest.cc',
           'api/sync_change_unittest.cc',
           'api/sync_data_unittest.cc',
           'api/sync_error_unittest.cc',
           'api/sync_merge_result_unittest.cc',
         ],
       },
     },
 
     # The unit test executable for sync tests.
@@ skipping 190 matching lines @@
           ],
           'variables': {
             'test_suite_name': 'sync_unit_tests',
           },
           'includes': [ '../build/apk_test.gypi' ],
         },
       ],
     }],
   ],
 }