Make HistoryDBTask not refcounted, and ensure it's destroyed on its origin thread.

chrome/browser/history/history_db_task.h

Index: chrome/browser/history/history_db_task.h
diff --git a/chrome/browser/history/history_db_task.h b/chrome/browser/history/history_db_task.h
index 4e0d8114ef71c601b766151743326af5f3c68a72..e96c5910f1aaf7dc6831f1219a60c80a5c0f3799 100644
--- a/chrome/browser/history/history_db_task.h
+++ b/chrome/browser/history/history_db_task.h
@@ -5,8 +5,6 @@
 #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;
@@ -17,8 +15,10 @@ class HistoryDatabase;
 // 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.

[sky, 2014/07/14 20:27:44]

Document where destruction occurs.

[Bernhard Bauer, 2014/07/15 10:17:24]

Done.

-class HistoryDBTask : public base::RefCountedThreadSafe<HistoryDBTask> {
+class 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
@@ -30,11 +30,6 @@ class HistoryDBTask : public base::RefCountedThreadSafe<HistoryDBTask> {
   // 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