Add ScrollTree::FindNodeFromElementId

cc/trees/property_tree.cc

 // Copyright 2014 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 <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 1207 matching lines @@
 
 #if DCHECK_IS_ON()
 void ScrollTree::CopyCompleteTreeState(const ScrollTree& other) {
   currently_scrolling_node_id_ = other.currently_scrolling_node_id_;
   layer_id_to_scroll_offset_map_ = other.layer_id_to_scroll_offset_map_;
   layer_id_to_synced_scroll_offset_map_ =
       other.layer_id_to_synced_scroll_offset_map_;
 }
 #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();
 
   if (property_trees()->is_main_thread) {
     currently_scrolling_node_id_ = kInvalidNodeId;
     layer_id_to_scroll_offset_map_.clear();
   }
 
 #if DCHECK_IS_ON()
   ScrollTree tree;
@@ skipping 908 matching lines @@
   const EffectNode* effect_node = effect_tree.Node(effect_id);
 
   if (effect_node->surface_contents_scale.x() != 0.0 &&
       effect_node->surface_contents_scale.y() != 0.0)
     screen_space_transform.Scale(1.0 / effect_node->surface_contents_scale.x(),
                                  1.0 / effect_node->surface_contents_scale.y());
   return screen_space_transform;
 }
 
 }  // namespace cc