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 fee2d6c61e4f92a745574b96d3008c01245076af..49e449809e1d559b3407a61d088fbb47f8f48b04 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1358,6 +1358,14 @@ 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);