Add UMA for CrossFadeAnimation.

ash/rotator/screen_rotation_animator.cc

Index: ash/rotator/screen_rotation_animator.cc
diff --git a/ash/rotator/screen_rotation_animator.cc b/ash/rotator/screen_rotation_animator.cc
index 31a54537dd859ca1f3d8535baabb1442e81af0d6..258e7b42fa6c618c6f3c919270109c00288f201d 100644
--- a/ash/rotator/screen_rotation_animator.cc
+++ b/ash/rotator/screen_rotation_animator.cc
@@ -150,8 +150,8 @@ std::unique_ptr<ui::LayerOwner> CreateBlackMaskLayerOwner(
 class ScreenRotationAnimationMetricsReporter
     : public ui::AnimationMetricsReporter {
  public:
-  ScreenRotationAnimationMetricsReporter() {}
-  ~ScreenRotationAnimationMetricsReporter() override {}
+  ScreenRotationAnimationMetricsReporter() = default;
+  ~ScreenRotationAnimationMetricsReporter() override = default;
 
   void Report(int value) override {
     UMA_HISTOGRAM_PERCENTAGE("Ash.Rotation.AnimationSmoothness", value);