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

chrome/browser/prerender/prerender_local_predictor.cc

 // 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.
 
 #include "chrome/browser/prerender/prerender_local_predictor.h"
 
 #include <ctype.h>
 
 #include <algorithm>
 #include <map>
@@ skipping 537 matching lines @@
       lookup_info->MaybeAddCandidateURLFromLocalData(it->first, priority);
     }
   }
 
   RecordEvent(EVENT_START_URL_LOOKUP);
   HistoryService* history = GetHistoryIfExists();
   if (history) {
     RecordEvent(EVENT_GOT_HISTORY_ISSUING_LOOKUP);
     CandidatePrerenderInfo* lookup_info_ptr = lookup_info.get();
     history->ScheduleDBTask(
-        new GetURLForURLIDTask(lookup_info_ptr,
-                               base::Bind(&PrerenderLocalPredictor::OnLookupURL,
-                                          base::Unretained(this),
-                                          base::Passed(&lookup_info))),
+        scoped_ptr<history::HistoryDBTask>(
+            new GetURLForURLIDTask(
+                lookup_info_ptr,
+                base::Bind(&PrerenderLocalPredictor::OnLookupURL,
+                           base::Unretained(this),
+                           base::Passed(&lookup_info)))),
         &history_db_tracker_);
   }
 }
 
 void PrerenderLocalPredictor::OnLookupURL(
     scoped_ptr<CandidatePrerenderInfo> info) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   RecordEvent(EVENT_PRERENDER_URL_LOOKUP_RESULT);
 
@@ skipping 419 matching lines @@
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   RecordEvent(EVENT_INIT_STARTED);
   Profile* profile = prerender_manager_->profile();
   if (!profile || DisableLocalPredictorBasedOnSyncAndConfiguration(profile)) {
     RecordEvent(EVENT_INIT_FAILED_UNENCRYPTED_SYNC_NOT_ENABLED);
     return;
   }
   HistoryService* history = GetHistoryIfExists();
   if (history) {
     CHECK(!is_visit_database_observer_);
-    history->ScheduleDBTask(new GetVisitHistoryTask(this, kMaxVisitHistory),
-                            &history_db_tracker_);
+    history->ScheduleDBTask(
+        scoped_ptr<history::HistoryDBTask>(
+            new GetVisitHistoryTask(this, kMaxVisitHistory)),
+        &history_db_tracker_);
     history->AddVisitDatabaseObserver(this);
     is_visit_database_observer_ = true;
   } else {
     RecordEvent(EVENT_INIT_FAILED_NO_HISTORY);
   }
 }
 
 void PrerenderLocalPredictor::OnPLTEventForURL(const GURL& url,
                                                base::TimeDelta page_load_time) {
   scoped_ptr<PrerenderProperties> prerender;
@@ skipping 402 matching lines @@
       break;
     case content::SessionStorageNamespace::MERGE_RESULT_MERGEABLE:
       RecordEvent(EVENT_NAMESPACE_MISMATCH_MERGE_RESULT_MERGEABLE);
       break;
     default:
       NOTREACHED();
   }
 }
 
 }  // namespace prerender