Flip the flag to enable smooth screen rotation by default.

ash/rotator/test/screen_rotation_animator_test_api.h

 // Copyright 2017 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_TEST_SCREEN_ROTATION_ANIMATOR_TEST_API_H_
 #define ASH_ROTATOR_TEST_SCREEN_ROTATION_ANIMATOR_TEST_API_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 15 matching lines @@
 class ScreenRotationAnimatorTestApi
     : public ui::test::MultiLayerAnimatorTestController,
       public ui::test::MultiLayerAnimatorTestControllerDelegate {
  public:
   explicit ScreenRotationAnimatorTestApi(ScreenRotationAnimator* animator);
   ~ScreenRotationAnimatorTestApi() override;
 
   // Wrapper functions for ScreenRotationAnimator.
   ui::Layer* GetOldLayerTreeRootLayer();
   void DisableAnimationTimers();
+  void SetEnableAnimation(bool enable);
 
  private:
   // MultiLayerAnimatorTestControllerDelegate:
   std::vector<ui::LayerAnimator*> GetLayerAnimators() override;
 
   ScreenRotationAnimator* animator_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimatorTestApi);
 };
 
 }  // namespace test
 }  // namespace ash
 
 #endif  // ASH_ROTATOR_TEST_SCREEN_ROTATION_ANIMATOR_TEST_API_H_