Port HistoryService::ScheduleDBTask to CancelableTaskTracker

chrome/browser/history/history_marshaling.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.
 
 // Data structures for communication between the history service on the main
 // thread and the backend on the history thread.
 
 #ifndef CHROME_BROWSER_HISTORY_HISTORY_MARSHALING_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_MARSHALING_H_
 
 #include "base/memory/scoped_vector.h"
 #include "chrome/browser/common/cancelable_request.h"
 #include "chrome/browser/history/history_service.h"
 #include "chrome/browser/history/page_usage_data.h"
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/history/history_marshaling_android.h"
 #endif
 
 namespace history {
 
 // Querying -------------------------------------------------------------------
 
 typedef CancelableRequest1<HistoryService::QueryMostVisitedURLsCallback,
                            history::MostVisitedURLList>
     QueryMostVisitedURLsRequest;
 
-// Generic operations ---------------------------------------------------------
-
-// The argument here is an input value, which is the task to run on the
-// background thread. The callback is used to execute the portion of the task
-// that executes on the main thread.
-typedef CancelableRequest1<base::Closure, scoped_refptr<HistoryDBTask> >
-    HistoryDBTaskRequest;
-
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_HISTORY_MARSHALING_H_