Switch BaseSessionService to use SequencedWorkerPool instead of FILE thread

chrome/browser/sessions/base_session_service.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 CHROME_BROWSER_SESSIONS_BASE_SESSION_SERVICE_H_
 #define CHROME_BROWSER_SESSIONS_BASE_SESSION_SERVICE_H_
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/gtest_prod_util.h"
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/common/cancelable_request.h"
 #include "chrome/browser/sessions/session_id.h"
 #include "chrome/common/cancelable_task_tracker.h"
 #include "url/gurl.h"
 
 class Profile;
 class SessionBackend;
 class SessionCommand;
 
 namespace sessions {
@@ skipping 121 matching lines @@
   // Returns true if the entry at specified |url| should be written to disk.
   bool ShouldTrackEntry(const GURL& url);
 
   // Invokes SessionBackend::ReadLastSessionCommands with callback on the
   // backend thread.
   // If testing, SessionBackend::ReadLastSessionCommands is invoked directly.
   CancelableTaskTracker::TaskId ScheduleGetLastSessionCommands(
       const InternalGetCommandsCallback& callback,
       CancelableTaskTracker* tracker);
 
-  // In production, this posts the task to the FILE thread.  For
+  // In production, this posts the task to the SequencedWorkerPool.  For
   // tests, it immediately runs the specified task on the current
   // thread.
   bool RunTaskOnBackendThread(const tracked_objects::Location& from_here,
                               const base::Closure& task);
 
   // Returns true if we appear to be running in production, false if we appear
-  // to be running as part of a unit test or if the FILE thread has gone away.
+  // to be running as part of a unit test or if the SequencedWorkerPool has
+  // been asked to shutdown.
   bool RunningInProduction() const;
 
   // Max number of navigation entries in each direction we'll persist.
   static const int max_persist_navigation_count;
 
  private:
   friend class BetterSessionRestoreCrashTest;
 
   // The profile. This may be null during testing.
   Profile* profile_;
 
   // The backend.
   scoped_refptr<SessionBackend> backend_;
 
   // Used to invoke Save.
   base::WeakPtrFactory<BaseSessionService> weak_factory_;
 
   // Commands we need to send over to the backend.
   std::vector<SessionCommand*>  pending_commands_;
 
   // Whether the backend file should be recreated the next time we send
   // over the commands.
   bool pending_reset_;
 
   // The number of commands sent to the backend before doing a reset.
   int commands_since_reset_;
 
+  // A token to make sure that all tasks will be serialized.
+  base::SequencedWorkerPool::SequenceToken sequence_token_;
+
   DISALLOW_COPY_AND_ASSIGN(BaseSessionService);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_BASE_SESSION_SERVICE_H_