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

ash/utility/transformer_util.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/utility/transformer_util.h"
+
+#include <cmath>
+
+#include "third_party/skia/include/core/SkMatrix44.h"
+#include "ui/gfx/transform.h"
+
+namespace ash {
+
+// Round near zero value to zero.
+void RoundNearZero(gfx::Transform* transform) {
+  const float kEpsilon = 0.001f;
+  SkMatrix44& matrix = transform->matrix();
+  for (int x = 0; x < 4; ++x) {
+    for (int y = 0; y < 4; ++y) {
+      if (std::abs(SkMScalarToFloat(matrix.get(x, y))) < kEpsilon)
+        matrix.set(x, y, SkFloatToMScalar(0.0f));
+    }
+  }
+}
+
+gfx::Transform CreateRotationTransform(display::Display::Rotation old_rotation,
+                                       display::Display::Rotation new_rotation,
+                                       const display::Display& display) {
+  const int rotation_angle = 90 * (((new_rotation - old_rotation) + 4) % 4);
+  gfx::Transform rotate;
+  // The origin is (0, 0), so the translate width/height must be reduced by
+  // 1 pixel.
+  float one_pixel = 1.0f / display.device_scale_factor();
+  switch (rotation_angle) {
+    case 0:
+      break;
+    case 90:
+      rotate.Translate(display.bounds().height() - one_pixel, 0);
+      rotate.Rotate(90);
+      break;
+    case 180:
+      rotate.Translate(display.bounds().width() - one_pixel,
+                       display.bounds().height() - one_pixel);
+      rotate.Rotate(180);
+      break;
+    case 270:
+      rotate.Translate(0, display.bounds().width() - one_pixel);
+      rotate.Rotate(270);
+      break;
+  }
+
+  RoundNearZero(&rotate);
+  return rotate;
+}
+
+}  // namespace ash