The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf

commit b2cf8f80ac8a98bff39300e3b1465012eaa5abdf
Author: a-v-y <a-v-y@yandex-team.ru>
Date: Sun Dec 11 17:35:07 2016

Remove duplicated user_prefs::TestingPrefServiceSyncable

In https://codereview.chromium.org/2479113002/ it was discovered that
current codebase has two duplicate TestingPrefServiceSyncable classes.
One in component/sync_preferences and another in
components/pref_registry. The decision from discussion is to delete the
one in components/pref_registry.

BUG= 672900 

R=gab@chromium.org, vasilii@chromium.org, hashimoto@chromium.org, pkasting@chromium.org, rdevlin.cronin@chromium.org, ben@chromium.org, blundell@chromium.org

TBR=rdevlin.cronin@chromium.org, ben@chromium.org, blundell@chromium.org

Review-Url: https://codereview.chromium.org/2562733003
Cr-Commit-Position: refs/heads/master@{#437790}

[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/chrome/browser/chromeos/fileapi/external_file_url_request_job_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/chrome/browser/chromeos/proxy_config_service_impl_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/chrome/test/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/content_settings/core/browser/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/content_settings/core/browser/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/content_settings/core/browser/cookie_settings_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/dom_distiller/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/dom_distiller/core/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/dom_distiller/core/distilled_page_prefs_unittests.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/dom_distiller/core/dom_distiller_request_view_base_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/dom_distiller/standalone/content_extractor_browsertest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/feedback/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/feedback/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/feedback/feedback_uploader_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/invalidation/impl/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/invalidation/impl/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/invalidation/impl/invalidator_storage_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/invalidation/impl/ticl_profile_settings_provider_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/ntp_tiles/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/ntp_tiles/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/ntp_tiles/popular_sites_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/password_manager/sync/browser/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/password_manager/sync/browser/password_manager_setting_migrator_service_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/password_manager/sync/browser/sync_username_test_base.h
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/pref_registry/BUILD.gn
[delete] https://crrev.com/d0972641a4a11586b44a621563e76d0c58f4595f/components/pref_registry/testing_pref_service_syncable.cc
[delete] https://crrev.com/d0972641a4a11586b44a621563e76d0c58f4595f/components/pref_registry/testing_pref_service_syncable.h
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/search_engines/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/search_engines/default_search_manager_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/search_engines/default_search_pref_migration_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/search_engines/template_url_prepopulate_data_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/signin/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/signin/core/browser/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/signin/core/browser/account_investigator_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/signin/core/browser/signin_header_helper_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/signin/ios/browser/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/signin/ios/browser/account_consistency_service_unittest.mm
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/suggestions/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/suggestions/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/suggestions/blacklist_store_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/suggestions/suggestions_store_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/sync/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/sync/base/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/sync/base/sync_prefs_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/translate/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/translate/core/browser/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/translate/core/browser/translate_manager_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/translate/core/browser/translate_prefs_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/translate/core/browser/translate_ranker_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/components/translate/core/browser/translate_ui_delegate_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/extensions/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/extensions/browser/BUILD.gn
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/extensions/browser/DEPS
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/extensions/browser/api/runtime/restart_after_delay_api_unittest.cc
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/extensions/browser/api_unittest.h
[modify] https://crrev.com/b2cf8f80ac8a98bff39300e3b1465012eaa5abdf/extensions/browser/lazy_background_task_queue_unittest.cc

I believe that #1 addresses the issue completely.
a-v-y@ -- please reopen or e-mail me if you disagree. Also, thanks for your work on this!