Handle new screen rotation request while waiting for the copy request callback.

ash/rotator/screen_rotation_animator.h

Index: ash/rotator/screen_rotation_animator.h
diff --git a/ash/rotator/screen_rotation_animator.h b/ash/rotator/screen_rotation_animator.h
index 4c219222ab3a97226b8a5c7ee44c6b4da717131c..ce77673d356d949614e4d4f6714cc5ee5bc0b357 100644
--- a/ash/rotator/screen_rotation_animator.h
+++ b/ash/rotator/screen_rotation_animator.h
@@ -64,9 +64,11 @@ class ASH_EXPORT ScreenRotationAnimator {
   using CopyCallback =
       base::Callback<void(std::unique_ptr<cc::CopyOutputResult> result)>;
   struct ScreenRotationRequest {
-    ScreenRotationRequest(display::Display::Rotation to_rotation,
+    ScreenRotationRequest(int64_t id,
+                          display::Display::Rotation to_rotation,
                           display::Display::RotationSource from_source)
-        : new_rotation(to_rotation), source(from_source) {}
+        : id(id), new_rotation(to_rotation), source(from_source) {}
+    int64_t id;
     display::Display::Rotation new_rotation;
     display::Display::RotationSource source;
   };
@@ -123,6 +125,10 @@ class ASH_EXPORT ScreenRotationAnimator {
   };
   ScreenRotationState screen_rotation_state_;
 
+  // Rotation request id, used to ignore copy request callback if we decide to
+  // cancel the previous rotation request.
+  int64_t rotation_request_id_;
+
   std::unique_ptr<ui::AnimationMetricsReporter> metrics_reporter_;
   // Only set in unittest to disable animation timers.
   bool disable_animation_timers_for_test_;