Do not observe MessageLoop destruction from ModelSafeWorker.

components/sync/driver/glue/ui_model_worker_unittest.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 "components/sync/driver/glue/ui_model_worker.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/location.h"
 #include "base/memory/ref_counted.h"
@@ skipping 18 matching lines @@
 // Converts |work| to a WorkCallback that will verify that it's run on the
 // thread it was constructed on.
 WorkCallback ClosureToWorkCallback(base::Closure work) {
   return base::Bind(&DoWork, base::ThreadTaskRunnerHandle::Get(), work);
 }
 
 class SyncUIModelWorkerTest : public testing::Test {
  public:
   SyncUIModelWorkerTest() : sync_thread_("SyncThreadForTest") {
     sync_thread_.Start();
-    worker_ = new UIModelWorker(base::ThreadTaskRunnerHandle::Get(), nullptr);
+    worker_ = new UIModelWorker(base::ThreadTaskRunnerHandle::Get());
   }
 
   void PostWorkToSyncThread(WorkCallback work) {
     sync_thread_.task_runner()->PostTask(
         FROM_HERE,
         base::Bind(base::IgnoreResult(&UIModelWorker::DoWorkAndWaitUntilDone),
                    worker_, work));
   }
 
  private:
   base::MessageLoop ui_loop_;
   base::Thread sync_thread_;
   scoped_refptr<UIModelWorker> worker_;
 };
 
 TEST_F(SyncUIModelWorkerTest, ScheduledWorkRunsOnUILoop) {
   base::RunLoop run_loop;
   PostWorkToSyncThread(ClosureToWorkCallback(run_loop.QuitClosure()));
   // This won't quit until the QuitClosure is run.
   run_loop.Run();
 }
 
 }  // namespace
 }  // namespace syncer