[SyncFS] Clean up SequencedWorkerPool in SyncEngineTest

chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.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 "chrome/browser/sync_file_system/drive_backend/sync_engine.h"
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/thread_task_runner_handle.h"
@@ skipping 55 matching lines @@
     sync_engine_->SetSyncEnabled(true);
     sync_engine_->OnReadyToSendRequests();
 
     WaitForWorkerTaskRunner();
   }
 
   virtual void TearDown() OVERRIDE {
     sync_engine_.reset();
     WaitForWorkerTaskRunner();
     worker_pool_->Shutdown();
+
+    worker_task_runner_ = NULL;
+    worker_pool_ = NULL;
+
     base::RunLoop().RunUntilIdle();
   }
 
   bool FindOriginStatus(const GURL& origin, std::string* status) {
     scoped_ptr<RemoteOriginStatusMap> status_map;
     sync_engine()->GetOriginStatusMap(CreateResultReceiver(&status_map));
     WaitForWorkerTaskRunner();
 
     RemoteOriginStatusMap::const_iterator itr = status_map->find(origin);
     if (itr == status_map->end())
@@ skipping 139 matching lines @@
 TEST_F(SyncEngineTest, ProcessRemoteChange) {
   SyncStatusCode sync_status;
   storage::FileSystemURL url;
   sync_engine()->ProcessRemoteChange(CreateResultReceiver(&sync_status, &url));
   WaitForWorkerTaskRunner();
   EXPECT_EQ(SYNC_STATUS_OK, sync_status);
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system