Fix black background when locking with fullscreen window:

ui/base/animation/animation_container_test_helper.h

+// Copyright (c) 2011 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 UI_BASE_ANIMATION_ANIMATION_CONTAINER_TEST_HELPER_H_
+#define UI_BASE_ANIMATION_ANIMATION_CONTAINER_TEST_HELPER_H_
+
+#include "base/test/scoped_time_controller.h"
+#include "base/time.h"
+#include "ui/base/animation/animation_container.h"
+#include "ui/base/ui_export.h"
+
+namespace ui {
+namespace test {
+
+// This class can be used in tests for fine control over animations.
+
+class AnimationContainerTestHelper {
+ public:
+  // Creates helper for given container. Container is now driven by this
+  // helper rather than by internal timer.
+  explicit AnimationContainerTestHelper(AnimationContainer* container);
+
+  ~AnimationContainerTestHelper();
+
+  // Advances AnimationContainer for |delta|.
+  void Advance(base::TimeDelta delta);
+
+  // Returns if AnimationContainer is animating.
+  bool IsAnimating();
+
+  // Forwards in large steps (1 second) while there are any animations running.
+  // Use it before deleting Helper to avoid negative time delta in animations
+  // once timer gets cleaned up.
+  void AdvanceUntilDone();
+
+ private:
+  AnimationContainer* container_;
+
+  base::test::ScopedTimeController time_controller_;
+
+  DISALLOW_COPY_AND_ASSIGN(AnimationContainerTestHelper);
+};
+
+}  // namespace test
+}  // namespace ui
+
+#endif  // UI_BASE_ANIMATION_ANIMATION_CONTAINER_TEST_HELPER_H_