Flip the flag to enable smooth screen rotation by default.

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 1a479280034c08281d14862a1f83a94a744594c0..71295561252e8fc8fe30e53c6952231ab165c0bf 100644
--- a/ash/rotator/screen_rotation_animator.h
+++ b/ash/rotator/screen_rotation_animator.h
@@ -66,6 +66,8 @@ class ASH_EXPORT ScreenRotationAnimator {
   // notifies |screen_rotation_animator_observer_|.
   void ProcessAnimationQueue();
 
+  bool CanAnimate() const { return enable_animation_; }
+
  protected:
   using CopyCallback =
       base::Callback<void(std::unique_ptr<cc::CopyOutputResult> result)>;
@@ -148,6 +150,10 @@ class ASH_EXPORT ScreenRotationAnimator {
     disable_animation_timers_for_test_ = disable_timers;
   }
 
+  void set_enable_animation_for_test(bool enable_animation) {
+    enable_animation_ = enable_animation;
+  }
+
   void StopAnimating();
 
   // The id of the display to rotate.
@@ -170,13 +176,15 @@ class ASH_EXPORT ScreenRotationAnimator {
   std::unique_ptr<ui::AnimationMetricsReporter> metrics_reporter_;
   // Only set in unittest to disable animation timers.
   bool disable_animation_timers_for_test_;
+  // Enables or disables animation.
+  bool enable_animation_;
   base::ObserverList<ScreenRotationAnimatorObserver>
       screen_rotation_animator_observers_;
   std::unique_ptr<ui::LayerTreeOwner> old_layer_tree_owner_;
   std::unique_ptr<ui::LayerTreeOwner> new_layer_tree_owner_;
   std::unique_ptr<ui::LayerOwner> black_mask_layer_owner_;
   std::unique_ptr<ScreenRotationRequest> last_pending_request_;
-  bool has_switch_ash_enable_smooth_screen_rotation_;
+  bool has_switch_ash_disable_smooth_screen_rotation_;
   aura::Window* root_window_;
   ui::Layer* screen_rotation_container_layer_;
   base::WeakPtrFactory<ScreenRotationAnimator> weak_factory_;