Flip the flag to enable smooth screen rotation by default.

ash/test/display_configuration_controller_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_TEST_DISPLAY_CONFIGURATION_CONTROLLER_TEST_API_H_
 #define ASH_TEST_DISPLAY_CONFIGURATION_CONTROLLER_TEST_API_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 
 namespace ash {
 class DisplayConfigurationController;
 class ScreenRotationAnimator;
 
 namespace test {
 
 // Accesses private data from a DisplayConfigurationController for testing.
 class DisplayConfigurationControllerTestApi {
  public:
   explicit DisplayConfigurationControllerTestApi(
       DisplayConfigurationController* controller);
 
   // Wrapper functions for DisplayConfigurationController.
   void DisableDisplayAnimator();
   int DisplayScreenRotationAnimatorMapSize();
   ScreenRotationAnimator* GetScreenRotationAnimatorForDisplay(
       int64_t display_id);
+  void SetEnableScreenRotationAnimator(int64_t display_id, bool enable);
 
  private:
   DisplayConfigurationController* controller_;
 
   DISALLOW_COPY_AND_ASSIGN(DisplayConfigurationControllerTestApi);
 };
 
 }  // namespace test
 }  // namespace ash
 
 #endif  // ASH_TEST_DISPLAY_CONFIGURATION_CONTROLLER_TEST_API_H_