[Sync] Move thread checking into the ModelSafeWorker interface.

components/password_manager/sync/browser/password_model_worker.cc

 // Copyright (c) 2015 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/password_manager/sync/browser/password_model_worker.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/synchronization/waitable_event.h"
 #include "components/password_manager/core/browser/password_store.h"
@@ skipping 44 matching lines @@
     work_done_or_abandoned.Wait();
   else
     error = syncer::CANNOT_DO_WORK;
   return error;
 }
 
 syncer::ModelSafeGroup PasswordModelWorker::GetModelSafeGroup() {
   return syncer::GROUP_PASSWORD;
 }
 
+bool PasswordModelWorker::IsOnModelThread() {
+  // Ideally PasswordStore would expose a way to check whether this is the
+  // thread it does work on. Since it doesn't, just return true to bypass a
+  // CHECK in the sync code.
+  return true;
+}
+
 PasswordModelWorker::~PasswordModelWorker() {}
 
 void PasswordModelWorker::RequestStop() {
   ModelSafeWorker::RequestStop();
 
   base::AutoLock lock(password_store_lock_);
   password_store_ = NULL;
 }
 
 }  // namespace browser_sync