Revert of Remove header dependencies from sequence_checker.h to sequenced_worker_pool.h

components/history/core/browser/expire_history_backend.h

 // Copyright (c) 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.
 
 #ifndef COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_
 
 #include <memory>
 #include <queue>
 #include <set>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "components/history/core/browser/history_types.h"
 
 class GURL;
 class TestingProfile;
 
-namespace base {
-class SequencedTaskRunner;
-}
-
 namespace history {
 
 class HistoryBackendClient;
 class HistoryBackendNotifier;
 class HistoryDatabase;
 class ThumbnailDatabase;
 
 // Encapsulates visit expiration criteria and type of visits to expire.
 class ExpiringVisitsReader {
  public:
@@ skipping 227 matching lines @@
   // Used to generate runnable methods to do timers on this class. They will be
   // automatically canceled when this class is deleted.
   base::WeakPtrFactory<ExpireHistoryBackend> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExpireHistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_