Revert "Sync: Avoid deadlock in SyncBackendRegistrar / ModelSafeWorker on sync backend shutdown."

chrome/browser/sync/glue/password_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 "chrome/browser/sync/glue/password_model_worker.h"
 
 #include "base/bind.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/waitable_event.h"
 #include "components/password_manager/core/browser/password_store.h"
@@ skipping 46 matching lines @@
 
 void PasswordModelWorker::CallDoWorkAndSignalTask(
     const syncer::WorkCallback& work,
     WaitableEvent* done,
     syncer::SyncerError *error) {
   *error = work.Run();
   done->Signal();
 }
 
 void PasswordModelWorker::RegisterForPasswordLoopDestruction() {
+  base::MessageLoop::current()->AddDestructionObserver(this);
   SetWorkingLoopToCurrent();
 }
 
 void PasswordModelWorker::RequestStop() {
   ModelSafeWorker::RequestStop();
 
   base::AutoLock lock(password_store_lock_);
   password_store_ = NULL;
 }
 
 }  // namespace browser_sync