Flip the flag to enable smooth screen rotation by default.

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"
@@ skipping 48 matching lines @@
   void AddScreenRotationAnimatorObserver(
       ScreenRotationAnimatorObserver* observer);
   void RemoveScreenRotationAnimatorObserver(
       ScreenRotationAnimatorObserver* observer);
 
   // 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();
 
+  bool CanAnimate() const { return enable_animation_; }
+
  protected:
   using CopyCallback =
       base::Callback<void(std::unique_ptr<cc::CopyOutputResult> result)>;
   struct ScreenRotationRequest {
     ScreenRotationRequest(int64_t id,
                           display::Display::Rotation to_rotation,
                           display::Display::RotationSource from_source)
         : id(id), new_rotation(to_rotation), source(from_source) {}
     int64_t id;
     display::Display::Rotation old_rotation;
@@ skipping 62 matching lines @@
   // 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);
 
   void set_disable_animation_timers_for_test(bool disable_timers) {
     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.
   int64_t display_id_;
 
   // 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_;
 
   // 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_;
+  // 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_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimator);
 };
 
 }  // namespace ash
 
 #endif  // ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_