cc : Track opacity animation changes on effect tree

cc/trees/property_tree.h

Index: cc/trees/property_tree.h
diff --git a/cc/trees/property_tree.h b/cc/trees/property_tree.h
index 8b94fe9c3bdcb67dedadb5e5ef2693bbdf699999..12ae31040f776ed86933485d92cf3605e19b2c57 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -271,6 +271,7 @@ struct CC_EXPORT EffectNodeData {
   bool double_sided;
   bool is_drawn;
   bool has_animated_opacity;
+  bool is_currently_animating_opacity;
   // We need to track changes to effects on the compositor to compute damage
   // rect.
   bool effect_changed;