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

chrome/browser/ui/search/instant_extended_interactive_uitest.cc

 // Copyright 2013 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 <sstream>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/statistics_recorder.h"
@@ skipping 209 matching lines @@
     return true;
   }
 
   void BlockUntilHistoryProcessesPendingRequests() {
     HistoryService* history = HistoryServiceFactory::GetForProfile(
         browser()->profile(), Profile::EXPLICIT_ACCESS);
     DCHECK(history);
     DCHECK(base::MessageLoop::current());
 
     base::CancelableTaskTracker tracker;
-    history->ScheduleDBTask(new QuittingHistoryDBTask(), &tracker);
+    history->ScheduleDBTask(
+        scoped_ptr<history::HistoryDBTask>(
+            new QuittingHistoryDBTask()),
+        &tracker);
     base::MessageLoop::current()->Run();
   }
 
   int CountSearchProviderSuggestions() {
     return omnibox()->model()->autocomplete_controller()->search_provider()->
         matches().size();
   }
 
   int on_most_visited_change_calls_;
   int most_visited_items_count_;
@@ skipping 733 matching lines @@
   stream << "link.href = \"" << result_url.spec() << "\";";
   stream << "document.body.appendChild(link);";
   stream << "link.click();";
   EXPECT_TRUE(content::ExecuteScript(contents, stream.str()));
 
   content::WaitForLoadStop(contents);
   std::string expected_title =
       "Referrer is " + instant_url().GetWithEmptyPath().spec();
   EXPECT_EQ(ASCIIToUTF16(expected_title), contents->GetTitle());
 }