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

components/sync/base/scoped_event_signal.cc

Index: components/sync/base/scoped_event_signal.cc
diff --git a/components/sync/base/scoped_event_signal.cc b/components/sync/base/scoped_event_signal.cc
new file mode 100644
index 0000000000000000000000000000000000000000..daaaa1db453f2c1ed56b3fd0c400837a45eb4944
--- /dev/null
+++ b/components/sync/base/scoped_event_signal.cc
@@ -0,0 +1,34 @@
+// Copyright 2016 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/base/scoped_event_signal.h"
+
+#include "base/logging.h"
+#include "base/synchronization/waitable_event.h"
+
+namespace syncer {
+
+ScopedEventSignal::ScopedEventSignal(base::WaitableEvent* event)
+    : event_(event) {
+  DCHECK(event_);
+}
+
+ScopedEventSignal::ScopedEventSignal(ScopedEventSignal&& other)
+    : event_(other.event_) {
+  other.event_ = nullptr;
+}
+
+ScopedEventSignal& ScopedEventSignal::operator=(ScopedEventSignal&& other) {
+  DCHECK(!event_);
+  event_ = other.event_;
+  other.event_ = nullptr;
+  return *this;
+}
+
+ScopedEventSignal::~ScopedEventSignal() {
+  if (event_)
+    event_->Signal();
+}
+
+}  // namespace syncer