Clarify property tree id-to-index map names.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 58351e92ca84f10f88c3ae27eccc5b4907586f5d..d66f10f6e9cfc4c141cb97f1b52910bf66ae722a 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -662,7 +662,7 @@ void LayerTreeImpl::UpdatePropertyTreeScrollingAndAnimationFromMainThread() {
     const int id = layer_id_to_opacity.first;
     if (property_trees_.IsInIdToIndexMap(PropertyTrees::TreeType::EFFECT, id)) {
       EffectNode* node = property_trees_.effect_tree.Node(
-          property_trees_.effect_id_to_index_map[id]);
+          property_trees_.layer_id_to_effect_node_index[id]);
       if (!node->is_currently_animating_opacity ||
           node->opacity == layer_id_to_opacity.second) {
         layer_ids_to_remove.push_back(id);
@@ -681,7 +681,7 @@ void LayerTreeImpl::UpdatePropertyTreeScrollingAndAnimationFromMainThread() {
     if (property_trees_.IsInIdToIndexMap(PropertyTrees::TreeType::TRANSFORM,
                                          id)) {
       TransformNode* node = property_trees_.transform_tree.Node(
-          property_trees_.transform_id_to_index_map[id]);
+          property_trees_.layer_id_to_transform_node_index[id]);
       if (!node->is_currently_animating ||
           node->local == layer_id_to_transform.second) {
         layer_ids_to_remove.push_back(id);
@@ -700,7 +700,7 @@ void LayerTreeImpl::UpdatePropertyTreeScrollingAndAnimationFromMainThread() {
     const int id = layer_id_to_filters.first;
     if (property_trees_.IsInIdToIndexMap(PropertyTrees::TreeType::EFFECT, id)) {
       EffectNode* node = property_trees_.effect_tree.Node(
-          property_trees_.effect_id_to_index_map[id]);
+          property_trees_.layer_id_to_effect_node_index[id]);
       if (!node->is_currently_animating_filter ||
           node->filters == layer_id_to_filters.second) {
         layer_ids_to_remove.push_back(id);