[Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

components/sync/engine/browser_thread_model_worker.cc

Index: components/sync/engine/browser_thread_model_worker.cc
diff --git a/components/sync/engine/browser_thread_model_worker.cc b/components/sync/engine/browser_thread_model_worker.cc
index 3b29d8505a09387f3950b52bc29fc0ca81b87f1c..a6d92c54d56cd14e69c57e83083991bed7815162 100644
--- a/components/sync/engine/browser_thread_model_worker.cc
+++ b/components/sync/engine/browser_thread_model_worker.cc
@@ -4,45 +4,22 @@
 
 #include "components/sync/engine/browser_thread_model_worker.h"
 
-#include "base/bind.h"
-#include "base/callback.h"
-#include "base/synchronization/waitable_event.h"
-
-using base::SingleThreadTaskRunner;
+#include <utility>
 
 namespace syncer {
 
 BrowserThreadModelWorker::BrowserThreadModelWorker(
-    const scoped_refptr<SingleThreadTaskRunner>& runner,
+    const scoped_refptr<base::SingleThreadTaskRunner>& runner,
     ModelSafeGroup group)
     : runner_(runner), group_(group) {}
 
-SyncerError BrowserThreadModelWorker::DoWorkAndWaitUntilDoneImpl(
-    const WorkCallback& work) {
-  SyncerError error = UNSET;
+void BrowserThreadModelWorker::ScheduleWork(base::OnceClosure work) {
   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;
+    std::move(work).Run();
+  } else {
+    runner_->PostTask(FROM_HERE, std::move(work));
   }
-  work_done_or_abandoned.Wait();
-  return error;
 }
 
 ModelSafeGroup BrowserThreadModelWorker::GetModelSafeGroup() {
@@ -55,14 +32,4 @@ bool BrowserThreadModelWorker::IsOnModelThread() {
 
 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