Fixes possible use after free in SessionService

chrome/browser/sessions/session_service_test_helper.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/sessions/session_service_test_helper.h"
 
 #include "base/memory/scoped_vector.h"
+#include "base/message_loop/message_loop.h"
 #include "chrome/browser/sessions/session_backend.h"
 #include "chrome/browser/sessions/session_service.h"
 #include "chrome/browser/sessions/session_types.h"
 #include "components/sessions/serialized_navigation_entry_test_helper.h"
 #include "components/sessions/session_id.h"
 #include "content/public/browser/browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using base::Time;
 
@@ skipping 86 matching lines @@
 SessionBackend* SessionServiceTestHelper::backend() {
   return service_->backend();
 }
 
 void SessionServiceTestHelper::SetService(SessionService* service) {
   service_.reset(service);
   // Execute IO tasks posted by the SessionService.
   content::BrowserThread::GetBlockingPool()->FlushForTesting();
 }
 
+void SessionServiceTestHelper::RunTaskOnBackendThread(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task) {
+  service_->RunTaskOnBackendThread(from_here, task);
+}