Add second copy request after screen rotation to flatten the layers in animation.

ash/utility/transformer_util.h

+// 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_TRANSFORMER_UTIL_H_
+#define ASH_TRANSFORMER_UTIL_H_
+
+#include "ash/ash_export.h"
+#include "ui/display/display.h"
+
+namespace gfx {
+class Transform;
+}
+
+namespace ash {
+
+// Creates rotation transform from |old_rotation| to |new_rotation| based on the
+// |display| info.
+ASH_EXPORT gfx::Transform CreateRotationTransform(
+    display::Display::Rotation old_rotation,
+    display::Display::Rotation new_rotation,
+    const display::Display& display);
+
+}  // namespace ash
+
+#endif  // ASH_TRANSFORMER_UTIL_H_