Revert 284958 "Make HistoryDBTask not refcounted, and ensure it'..."

trunk/src/chrome/browser/history/history_db_task.h

Index: trunk/src/chrome/browser/history/history_db_task.h
===================================================================
--- trunk/src/chrome/browser/history/history_db_task.h	(revision 285001)
+++ trunk/src/chrome/browser/history/history_db_task.h	(working copy)
@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_HISTORY_HISTORY_DB_TASK_H_
 #define CHROME_BROWSER_HISTORY_HISTORY_DB_TASK_H_
 
+#include "base/memory/ref_counted.h"
+
 namespace history {
 
 class HistoryBackend;
@@ -14,12 +16,9 @@
 // thread. HistoryDBTask is scheduled using HistoryService::ScheduleDBTask.
 // When HistoryBackend processes the task it invokes RunOnDBThread. Once the
 // task completes and has not been canceled, DoneRunOnMainThread is invoked back
-// on the main thread, after which this object is destroyed, also on the
-// main thread.
-class HistoryDBTask {
+// on the main thread.
+class HistoryDBTask : public base::RefCountedThreadSafe<HistoryDBTask> {
  public:
-  virtual ~HistoryDBTask() {}
-
   // Invoked on the database thread. The return value indicates whether the
   // task is done. A return value of true signals the task is done and
   // RunOnDBThread should NOT be invoked again. A return value of false
@@ -31,6 +30,11 @@
   // only invoked if the request was not canceled and returned true from
   // RunOnDBThread.
   virtual void DoneRunOnMainThread() = 0;
+
+ protected:
+  friend class base::RefCountedThreadSafe<HistoryDBTask>;
+
+  virtual ~HistoryDBTask() {}
 };
 
 }  // namespace history