Add ScrollTree::FindNodeFromElementId

cc/trees/property_tree.cc

Index: cc/trees/property_tree.cc
diff --git a/cc/trees/property_tree.cc b/cc/trees/property_tree.cc
index 280ecd000bffb759bce8db68e84e65719c3c146c..932725f47ee9661512acea28c262cf671a1455d5 100644
--- a/cc/trees/property_tree.cc
+++ b/cc/trees/property_tree.cc
@@ -1225,6 +1225,14 @@ void ScrollTree::CopyCompleteTreeState(const ScrollTree& other) {
 }
 #endif
 
+ScrollNode* ScrollTree::FindNodeFromElementId(ElementId id) {
+  auto iterator = property_trees()->element_id_to_scroll_node_index.find(id);
+  if (iterator == property_trees()->element_id_to_scroll_node_index.end())
+    return nullptr;
+
+  return Node(iterator->second);
+}
+
 void ScrollTree::clear() {
   PropertyTree<ScrollNode>::clear();