Fix corner case if another rotation request comes before the copy request finishes.

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 1852033b9e6b5c8aff54bd83d0a14275daf44adf..4c219222ab3a97226b8a5c7ee44c6b4da717131c 100644
--- a/ash/rotator/screen_rotation_animator.h
+++ b/ash/rotator/screen_rotation_animator.h
@@ -112,7 +112,17 @@ class ASH_EXPORT ScreenRotationAnimator {
 
   // The id of the display to rotate.
   int64_t display_id_;
-  bool is_rotating_;
+
+  // For current slow rotation animation, there are two states |ROTATING| and
+  // |IDLE|. For the smooth rotation animation, we need to send copy request
+  // and get copy result before animating.
+  enum ScreenRotationState {
+    COPY_REQUESTED,
+    ROTATING,
+    IDLE,
+  };
+  ScreenRotationState screen_rotation_state_;
+
   std::unique_ptr<ui::AnimationMetricsReporter> metrics_reporter_;
   // Only set in unittest to disable animation timers.
   bool disable_animation_timers_for_test_;