Add screen rotation animator lock.

ash/rotator/screen_rotation_animator_lock.h

Index: ash/rotator/screen_rotation_animator_lock.h
diff --git a/ash/rotator/screen_rotation_animator_lock.h b/ash/rotator/screen_rotation_animator_lock.h
new file mode 100644
index 0000000000000000000000000000000000000000..7c1a7a17212b59ff6393bcf54bd21ceaaa0fe433
--- /dev/null
+++ b/ash/rotator/screen_rotation_animator_lock.h
@@ -0,0 +1,35 @@
+// Copyright 2017 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.
+
+#ifndef ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_LOCK_H
+#define ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_LOCK_H
+
+#include "ash/ash_export.h"
+#include "base/memory/weak_ptr.h"
+
+namespace ash {
+
+class ScreenRotationAnimator;
+
+class ASH_EXPORT ScreenRotationAnimatorLock {
+ public:
+  explicit ScreenRotationAnimatorLock(
+      base::WeakPtr<ScreenRotationAnimator> animator);
+  ~ScreenRotationAnimatorLock();
+
+  void lock();
+
+  void unlock();
+
+  void TimeoutLock();
+
+ protected:
+  base::WeakPtr<ScreenRotationAnimator> animator_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimatorLock);
+};
+
+}  // namespace ash
+
+#endif  // ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_LOCK_H