Use a bitfield to store animatable properties.

ash/rotator/screen_rotation.cc

Index: ash/rotator/screen_rotation.cc
diff --git a/ash/rotator/screen_rotation.cc b/ash/rotator/screen_rotation.cc
index 9352d81ea342e0e47c7dd748a82e85595028422b..02b13a06ec982dc1c411186e5f4854ea784ee924 100644
--- a/ash/rotator/screen_rotation.cc
+++ b/ash/rotator/screen_rotation.cc
@@ -31,7 +31,7 @@ base::TimeDelta GetTransitionDuration(int degrees) {
 }  // namespace
 
 ScreenRotation::ScreenRotation(int degrees, ui::Layer* layer)
-    : ui::LayerAnimationElement(GetProperties(),
+    : ui::LayerAnimationElement(LayerAnimationElement::TRANSFORM,
                                 GetTransitionDuration(degrees)),
       degrees_(degrees) {
   InitTransform(layer);
@@ -120,13 +120,4 @@ void ScreenRotation::OnGetTarget(TargetValue* target) const {
 void ScreenRotation::OnAbort(ui::LayerAnimationDelegate* delegate) {
 }
 
-// static
-const ui::LayerAnimationElement::AnimatableProperties&
-ScreenRotation::GetProperties() {
-  static ui::LayerAnimationElement::AnimatableProperties properties;
-  if (properties.empty())
-    properties.insert(ui::LayerAnimationElement::TRANSFORM);
-  return properties;
-}
-
 }  // namespace ash