Add screen rotation animator lock.

ash/rotator/screen_rotation_animator_lock.cc

+// 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.
+
+#include "ash/rotator/screen_rotation_animator_lock.h"
+
+#include "ash/rotator/screen_rotation_animator.h"
+
+namespace ash {
+
+ScreenRotationAnimatorLock::ScreenRotationAnimatorLock(
+    base::WeakPtr<ScreenRotationAnimator> animator)
+    : animator_(animator) {}
+
+ScreenRotationAnimatorLock::~ScreenRotationAnimatorLock() {
+  unlock();
+}
+
+void ScreenRotationAnimatorLock::lock() {
+  if (animator_)
+    animator_->AddAnimatorLock(this);
+}
+
+void ScreenRotationAnimatorLock::unlock() {
+  if (animator_)
+    animator_->RemoveAnimatorLock(this);
+}
+
+void ScreenRotationAnimatorLock::TimeoutLock() {
+  unlock();
+  animator_ = nullptr;
+}
+
+}  // namespace ash