Uses copy request to flatten the layers to do screen rotation animation.

ash/rotator/screen_rotation_animator.h

 // Copyright 2015 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_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_
 #define ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_
 
 #include <stdint.h>
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "ui/display/display.h"
 
+namespace cc {
+class CopyOutputResult;
+}  // namespace cc
+
 namespace ui {
 class AnimationMetricsReporter;
 class Layer;
 class LayerTreeOwner;
 }  // namespace ui
 
 namespace ash {
 namespace test {
 class ScreenRotationAnimatorTestApi;
 }  // namespace test
@@ skipping 26 matching lines @@
 
   // When screen rotation animation is ended or aborted, calls |Rotate()| with
   // the pending rotation request if the request queue is not empty. Otherwise
   // notifies |screen_rotation_animator_observer_|.
   void ProcessAnimationQueue();
 
  private:
   friend class ash::test::ScreenRotationAnimatorTestApi;
   struct ScreenRotationRequest;
 
-  // Set the screen orientation to |new_rotation| and animate the change. The
+  void StartRotationAnimation(
+      std::unique_ptr<ScreenRotationRequest> rotation_request);
+
+  void RequestCopyRootLayerAndAnimateRotation(

[bruthig, 2017/03/30 18:28:24]

Some docs on these functions would be helpful.  Especially mentioning the ones
that are asynchronous.

[wutao, 2017/03/30 21:25:41]

Done.

+      std::unique_ptr<ScreenRotationRequest> rotation_request);
+
+  void OnRootLayerCopiedBeforeRotation(
+      std::unique_ptr<ScreenRotationRequest> rotation_request,
+      std::unique_ptr<cc::CopyOutputResult> result);
+
+  // Recreates all |root_window| layers.
+  void CreateOldLayerTree();
+
+  // Requests a copy of |root_window| root layer output.
+  void CopyOldLayerTree(std::unique_ptr<cc::CopyOutputResult> result);
+
+  // Sets the screen orientation to |new_rotation| and animate the change. The
   // animation will rotate the initial orientation's layer towards the new
   // orientation through |rotation_degrees| while fading out, and the new
   // orientation's layer will be rotated in to the |new_orientation| through
   // |rotation_degrees| arc.
   void AnimateRotation(std::unique_ptr<ScreenRotationRequest> rotation_request);

[bruthig, 2017/03/30 18:28:24]

It is a very subtle detail that AnimateRotation() now requires
|old_layer_tree_owner_| to be set up properly prior to being called. I see 2
ways to make this better:

1) Document it here.
2) Add a 'std::unique_ptr<ui::LayerTreeOwner> old_layer_tree_owner' parameter to
AnimateRotation() and pass it along from the CopyOldLayerTree() and
CreateOldLayerTree() functions. [CopyOldLayerTree() and CreateOldLayerTree()
could probably be moved to anonymous helper functions with this approach]

I have a slight preference for #2 but I'm ok with 1 too.

[wutao, 2017/03/30 21:25:41]

I prefer document it here first. In the further edition, when we add the second
copy output request, the function signature will change again. And at that time,
will consider to move some of the functions to anonymous namespace as well.

 
   void set_disable_animation_timers_for_test(bool disable_timers);
 
   void StopAnimating();
 
   // The id of the display to rotate.
   int64_t display_id_;
   bool is_rotating_;
   std::unique_ptr<ui::AnimationMetricsReporter> metrics_reporter_;
   // Only set in unittest to disable animation timers.
   bool disable_animation_timers_for_test_;
   base::ObserverList<ScreenRotationAnimatorObserver>
       screen_rotation_animator_observers_;
   std::unique_ptr<ui::LayerTreeOwner> old_layer_tree_owner_;
   std::unique_ptr<ScreenRotationRequest> last_pending_request_;
   base::WeakPtrFactory<ScreenRotationAnimator> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimator);
 };
 
 }  // namespace ash
 
 #endif  // ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_