Revert of Allow ObserverListThreadSafe to be used from sequenced tasks.

components/ntp_tiles/most_visited_sites_unittest.cc

 // Copyright 2015 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 "components/ntp_tiles/most_visited_sites.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <ostream>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/callback_list.h"
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "base/test/sequenced_worker_pool_owner.h"
-#include "base/threading/thread_task_runner_handle.h"
 #include "components/history/core/browser/top_sites.h"
 #include "components/history/core/browser/top_sites_observer.h"
 #include "components/ntp_tiles/icon_cacher.h"
 #include "components/ntp_tiles/json_unsafe_parser.h"
 #include "components/ntp_tiles/popular_sites_impl.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/ntp_tiles/switches.h"
 #include "components/sync_preferences/testing_pref_service_syncable.h"
 #include "net/url_request/test_url_fetcher_factory.h"
 #include "net/url_request/url_request_test_util.h"
@@ skipping 771 matching lines @@
                   MatchesTile("Site 4", "https://www.site4.com/",
                               NTPTileSource::TOP_SITES),
                   MatchesTile("Site 1", "https://www.site1.com/",
                               NTPTileSource::POPULAR),
                   MatchesTile("Site 2", "https://www.site2.com/",
                               NTPTileSource::POPULAR)));
 }
 
 }  // namespace
 }  // namespace ntp_tiles