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

components/sync/engine/ui_model_worker.cc

Index: components/sync/engine/ui_model_worker.cc
diff --git a/components/sync/engine/ui_model_worker.cc b/components/sync/engine/ui_model_worker.cc
index 08cc1a2502bbd09f396b756bc47bd070eca0782b..77fe9c7799a65db7437df9cc45edf62a0611467c 100644
--- a/components/sync/engine/ui_model_worker.cc
+++ b/components/sync/engine/ui_model_worker.cc
@@ -6,11 +6,90 @@
 
 #include <utility>
 
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/callback.h"
+#include "components/sync/base/scoped_event_signal.h"
+
 namespace syncer {
+
+namespace {
+
+class ScopedEventSignalWithWorker {
+ public:
+  ScopedEventSignalWithWorker(scoped_refptr<UIModelWorker> ui_model_worker,
+                              base::WaitableEvent* event)
+      : ui_model_worker_(std::move(ui_model_worker)),
+        scoped_event_signal_(event) {}
+
+  ScopedEventSignalWithWorker(ScopedEventSignalWithWorker&&) = default;
+  ScopedEventSignalWithWorker& operator=(ScopedEventSignalWithWorker&&) =
+      default;
+
+  bool IsStopped() const { return ui_model_worker_->IsStopped(); }
+
+ private:
+  // This reference prevents the event in |scoped_event_signal_| from being
+  // signaled after being deleted.
+  scoped_refptr<UIModelWorker> ui_model_worker_;
+
+  ScopedEventSignal scoped_event_signal_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedEventSignalWithWorker);
+};
+
+void CallDoWorkAndSignalEvent(
+    const WorkCallback& work,
+    ScopedEventSignalWithWorker scoped_event_signal_with_worker,
+    SyncerError* error_info) {
+  if (!scoped_event_signal_with_worker.IsStopped())
+    *error_info = work.Run();
+  // The event in |scoped_event_signal_with_worker| is signaled at the end of
+  // this scope.
+}
+
+}  // namespace
 
 UIModelWorker::UIModelWorker(
     scoped_refptr<base::SingleThreadTaskRunner> ui_thread)
-    : ui_thread_(std::move(ui_thread)) {}
+    : ui_thread_(std::move(ui_thread)),
+      work_done_or_abandoned_(base::WaitableEvent::ResetPolicy::MANUAL,
+                              base::WaitableEvent::InitialState::NOT_SIGNALED),
+      stop_requested_(base::WaitableEvent::ResetPolicy::MANUAL,
+                      base::WaitableEvent::InitialState::NOT_SIGNALED) {
+  sequence_checker_.DetachFromSequence();
+}
+
+SyncerError UIModelWorker::DoWorkAndWaitUntilDoneImpl(
+    const WorkCallback& work) {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+  DCHECK(!ui_thread_->BelongsToCurrentThread());
+
+  SyncerError error_info;
+  work_done_or_abandoned_.Reset();
+
+  if (!ui_thread_->PostTask(
+          FROM_HERE,
+          base::Bind(&CallDoWorkAndSignalEvent, work,
+                     base::Passed(syncer::ScopedEventSignalWithWorker(
+                         this, &work_done_or_abandoned_)),
+                     &error_info))) {
+    DLOG(WARNING) << "Could not post work to UI loop.";
+    error_info = CANNOT_DO_WORK;
+    return error_info;
+  }
+
+  base::WaitableEvent* events[] = {&work_done_or_abandoned_, &stop_requested_};
+  base::WaitableEvent::WaitMany(events, arraysize(events));
+
+  return error_info;
+}
+
+void UIModelWorker::RequestStop() {
+  DCHECK(ui_thread_->BelongsToCurrentThread());
+  ModelSafeWorker::RequestStop();
+  stop_requested_.Signal();
+}
 
 ModelSafeGroup UIModelWorker::GetModelSafeGroup() {
   return GROUP_UI;
@@ -22,8 +101,4 @@
 
 UIModelWorker::~UIModelWorker() {}
 
-void UIModelWorker::ScheduleWork(base::OnceClosure work) {
-  ui_thread_->PostTask(FROM_HERE, std::move(work));
-}
-
 }  // namespace syncer