Clarify property tree id-to-index map names.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 3935 matching lines @@
   PropertyTrees* property_trees = tree->property_trees();
   DCHECK(property_trees->IsInIdToIndexMap(PropertyTrees::TreeType::SCROLL,
                                           layer_id));
   DCHECK_EQ(
       1u, property_trees->element_id_to_transform_node_index.count(element_id));
   int transform_node_index =
       property_trees->element_id_to_transform_node_index[element_id];
   // TODO(wkorman): Build map from element id to scroll node in property tree
   // builder and make use of it below.
   const int scroll_node_index =
-      property_trees->scroll_id_to_index_map[layer_id];
+      property_trees->layer_id_to_scroll_node_index[layer_id];
   if (scroll_node_index != ScrollTree::kInvalidNodeId) {
     property_trees->scroll_tree.OnScrollOffsetAnimated(
         layer_id, transform_node_index, scroll_node_index, scroll_offset, tree);
     // Run mutation callbacks to respond to updated scroll offset.
     Mutate(CurrentBeginFrameArgs().frame_time);
   }
 }
 
 bool LayerTreeHostImpl::AnimationsPreserveAxisAlignment(
     const LayerImpl* layer) const {
@@ skipping 122 matching lines @@
       worker_context_visibility_ =
           worker_context->CacheController()->ClientBecameVisible();
     } else {
       worker_context->CacheController()->ClientBecameNotVisible(
           std::move(worker_context_visibility_));
     }
   }
 }
 
 }  // namespace cc