Do not observe MessageLoop destruction from ModelSafeWorker.

components/sync/driver/glue/browser_thread_model_worker.cc

 // Copyright 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/browser_thread_model_worker.h"
 
 #include "base/bind.h"
+#include "base/callback.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
 
 using base::SingleThreadTaskRunner;
 
 namespace syncer {
 
 BrowserThreadModelWorker::BrowserThreadModelWorker(
     const scoped_refptr<SingleThreadTaskRunner>& runner,
-    ModelSafeGroup group,
-    WorkerLoopDestructionObserver* observer)
-    : ModelSafeWorker(observer), runner_(runner), group_(group) {}
+    ModelSafeGroup group)
+    : runner_(runner), group_(group) {}
 
 SyncerError BrowserThreadModelWorker::DoWorkAndWaitUntilDoneImpl(
     const WorkCallback& work) {
   SyncerError error = UNSET;
   if (runner_->BelongsToCurrentThread()) {
     DLOG(WARNING) << "Already on thread " << runner_;
     return work.Run();
   }
 
   // Signaled when the task is deleted, i.e. after it runs or when it is
@@ skipping 15 matching lines @@
   work_done_or_abandoned.Wait();
   return error;
 }
 
 ModelSafeGroup BrowserThreadModelWorker::GetModelSafeGroup() {
   return group_;
 }
 
 BrowserThreadModelWorker::~BrowserThreadModelWorker() {}
 
-void BrowserThreadModelWorker::RegisterForLoopDestruction() {
-  if (runner_->BelongsToCurrentThread()) {
-    SetWorkingLoopToCurrent();
-  } else {
-    runner_->PostTask(
-        FROM_HERE,
-        Bind(&BrowserThreadModelWorker::RegisterForLoopDestruction, this));
-  }
-}
-
 void BrowserThreadModelWorker::CallDoWorkAndSignalTask(
     const WorkCallback& work,
     syncer::ScopedEventSignal scoped_event_signal,
     SyncerError* error) {
   DCHECK(runner_->BelongsToCurrentThread());
   if (!IsStopped())
     *error = work.Run();
   // The event in |scoped_event_signal| is signaled at the end of this scope.
 }
 
 }  // namespace syncer