[Sync] Move sync's ModelSafeWorker implementations to engine/.

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)
-    : 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
-  // abandoned.
-  base::WaitableEvent work_done_or_abandoned(
-      base::WaitableEvent::ResetPolicy::AUTOMATIC,
-      base::WaitableEvent::InitialState::NOT_SIGNALED);
-
-  if (!runner_->PostTask(
-          FROM_HERE,
-          base::Bind(
-              &BrowserThreadModelWorker::CallDoWorkAndSignalTask, this, work,
-              base::Passed(syncer::ScopedEventSignal(&work_done_or_abandoned)),
-              &error))) {
-    DLOG(WARNING) << "Failed to post task to runner " << runner_;
-    error = CANNOT_DO_WORK;
-    return error;
-  }
-  work_done_or_abandoned.Wait();
-  return error;
-}
-
-ModelSafeGroup BrowserThreadModelWorker::GetModelSafeGroup() {
-  return group_;
-}
-
-bool BrowserThreadModelWorker::IsOnModelThread() {
-  return runner_->BelongsToCurrentThread();
-}
-
-BrowserThreadModelWorker::~BrowserThreadModelWorker() {}
-
-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