cc : Track opacity animation changes on effect tree

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index f41bc9fea43e116e44e5cb744e9d05c65199a90c..8dcb80978c13370478006934aad47b50332eb892 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1361,6 +1361,14 @@ void LayerTreeHost::ElementTransformIsPotentiallyAnimatingChanged(
   layer->OnTransformIsPotentiallyAnimatingChanged(is_animating);
 }
 
+void LayerTreeHost::ElementOpacityIsCurrentlyAnimatingChanged(
+    ElementId element_id,
+    bool is_currently_animating) {
+  Layer* layer = LayerById(element_id);
+  DCHECK(layer);
+  layer->OnOpacityIsCurrentlyAnimatingChanged(is_currently_animating);
+}
+
 gfx::ScrollOffset LayerTreeHost::GetScrollOffsetForAnimation(
     ElementId element_id) const {
   Layer* layer = LayerById(element_id);