[Sync] Move thread checking into the ModelSafeWorker interface.

components/sync/test/engine/fake_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/test/engine/fake_model_worker.h"
 
 #include "base/callback.h"
 
 namespace syncer {
 
 FakeModelWorker::FakeModelWorker(ModelSafeGroup group) : group_(group) {}
 
 FakeModelWorker::~FakeModelWorker() {
   // We may need to relax this is FakeModelWorker is used in a
   // multi-threaded test; since ModelSafeWorkers are
   // RefCountedThreadSafe, they could theoretically be destroyed from
   // a different thread.
-  DCHECK(CalledOnValidThread());
+  DCHECK(thread_checker_.CalledOnValidThread());
 }
 
 SyncerError FakeModelWorker::DoWorkAndWaitUntilDoneImpl(
     const WorkCallback& work) {
-  DCHECK(CalledOnValidThread());
+  DCHECK(thread_checker_.CalledOnValidThread());
   // Simply do the work on the current thread.
   return work.Run();
 }
 
 ModelSafeGroup FakeModelWorker::GetModelSafeGroup() {
-  DCHECK(CalledOnValidThread());
+  DCHECK(thread_checker_.CalledOnValidThread());
   return group_;
 }
 
+bool FakeModelWorker::IsOnModelThread() {
+  return thread_checker_.CalledOnValidThread();
+}
+
 }  // namespace syncer