[ash-md] Remove the number of animators used for the Shelf animations.

ash/common/shelf/wm_shelf.cc

Index: ash/common/shelf/wm_shelf.cc
diff --git a/ash/common/shelf/wm_shelf.cc b/ash/common/shelf/wm_shelf.cc
index 72de8ab0b6881a0695e5444e13adaa419ebd8b68..f060648e2945acb9a55257f6d81e7f1f1ea2bc48 100644
--- a/ash/common/shelf/wm_shelf.cc
+++ b/ash/common/shelf/wm_shelf.cc
@@ -373,7 +373,7 @@ void WmShelf::OnAutoHideStateChanged(ShelfAutoHideState new_state) {
 }
 
 void WmShelf::OnBackgroundUpdated(ShelfBackgroundType background_type,
-                                  BackgroundAnimatorChangeType change_type) {
+                                  gfx::AnimationChangeType change_type) {
   if (background_type == GetBackgroundType())
     return;
   for (auto& observer : observers_)