Fix black background when locking with fullscreen window:

base/test/scoped_time_controller.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 BASE_TEST_SCOPED_TIME_CONTROLLER_H_
+#define BASE_TEST_SCOPED_TIME_CONTROLLER_H_
+
+#include "base/compiler_specific.h"
+#include "base/time.h"
+
+namespace base {
+namespace test {
+
+// TimeFactory that captures and freeses current time, and let to advance it
+// manually. Sets itself as a TimeFactory instance on construction, and
+// restores the previous one on destruction.
+// Use it with care, as it might break assumed time monotonicity after deletion.
+// The best way is to set it first in SetUp and remove it last at the
+// TearDown method.
+class ScopedTimeController : public base::TimeFactory {
+ public:
+  ScopedTimeController();
+  virtual ~ScopedTimeController();
+
+  // Advances inner time for |delta|. |Delta| have to be non-negative.
+  void Advance(base::TimeDelta delta);
+
+  // TimeFactory overrides
+  virtual base::Time TimeNow() OVERRIDE;
+  virtual base::TimeTicks TimeTicksNow() OVERRIDE;
+ private:
+  base::Time current_time_;
+  base::TimeTicks current_timeticks_;
+
+  base::TimeFactory* replaced_instance_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTimeController);
+};
+
+}  // namespace test
+}  // namespace base
+
+#endif  // BASE_TEST_SCOPED_TIME_CONTROLLER_H_