[SyncFS] Introduce CallbackTracker to handle callback abortion

chrome/chrome_tests_unit.gypi

 # Copyright 2012 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': [
     {
       # This target contains mocks and test utilities that don't belong in
       # production libraries but are used by more than one test executable.
       'target_name': 'test_support_common',
       'type': 'static_library',
@@ skipping 1355 matching lines @@
         'browser/sync/sync_error_notifier_ash_unittest.cc',
         'browser/sync/sync_global_error_unittest.cc',
         'browser/sync/sync_policy_handler_unittest.cc',
         'browser/sync/sync_startup_tracker_unittest.cc',
         'browser/sync/sync_ui_util_unittest.cc',
         'browser/sync/test/test_http_bridge_factory.cc',
         'browser/sync/test/test_http_bridge_factory.h',
         'browser/sync/test_profile_sync_service.cc',
         'browser/sync/test_profile_sync_service.h',
         'browser/sync_file_system/drive_backend/callback_helper_unittest.cc',
+        'browser/sync_file_system/drive_backend/callback_tracker_unittest.cc',
         'browser/sync_file_system/drive_backend/conflict_resolver_unittest.cc',
         'browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc',
         'browser/sync_file_system/drive_backend/drive_backend_test_util.cc',
         'browser/sync_file_system/drive_backend/drive_backend_test_util.h',
         'browser/sync_file_system/drive_backend/fake_drive_service_helper.cc',
         'browser/sync_file_system/drive_backend/fake_drive_service_helper.h',
         'browser/sync_file_system/drive_backend/fake_drive_uploader.cc',
         'browser/sync_file_system/drive_backend/fake_drive_uploader.h',
         'browser/sync_file_system/drive_backend/list_changes_task_unittest.cc',
         'browser/sync_file_system/drive_backend/local_to_remote_syncer_unittest.cc',
@@ skipping 1456 matching lines @@
             'unit_tests.isolate',
           ],
           'sources': [
             'unit_tests.isolate',
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }