Do not observe MessageLoop destruction from ModelSafeWorker.

components/sync/driver/glue/ui_model_worker.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 <utility>
+
 #include "base/bind.h"
 #include "base/bind_helpers.h"
-#include "base/message_loop/message_loop.h"
+#include "base/callback.h"
 #include "base/synchronization/waitable_event.h"
-#include "base/third_party/dynamic_annotations/dynamic_annotations.h"
-#include "base/threading/thread_restrictions.h"
 #include "components/sync/base/scoped_event_signal.h"
 
 namespace syncer {
 
 namespace {
 
 void CallDoWorkAndSignalEvent(const WorkCallback& work,
                               syncer::ScopedEventSignal scoped_event_signal,
                               SyncerError* error_info) {
   *error_info = work.Run();
   // The event in |scoped_event_signal| is signaled at the end of this scope.
 }
 
 }  // namespace
 
 UIModelWorker::UIModelWorker(
-    const scoped_refptr<base::SingleThreadTaskRunner>& ui_thread,
-    WorkerLoopDestructionObserver* observer)
-    : ModelSafeWorker(observer), ui_thread_(ui_thread) {}
-
-void UIModelWorker::RegisterForLoopDestruction() {
-  CHECK(ui_thread_->BelongsToCurrentThread());
-  SetWorkingLoopToCurrent();
-}
+    scoped_refptr<base::SingleThreadTaskRunner> ui_thread)
+    : ui_thread_(std::move(ui_thread)) {}
 
 SyncerError UIModelWorker::DoWorkAndWaitUntilDoneImpl(
     const WorkCallback& work) {
   SyncerError error_info;
   if (ui_thread_->BelongsToCurrentThread()) {
     DLOG(WARNING) << "DoWorkAndWaitUntilDone called from "
                   << "ui_loop_. Probably a nested invocation?";
     return work.Run();
   }
 
@@ skipping 17 matching lines @@
   return error_info;
 }
 
 ModelSafeGroup UIModelWorker::GetModelSafeGroup() {
   return GROUP_UI;
 }
 
 UIModelWorker::~UIModelWorker() {}
 
 }  // namespace syncer