Add map from element id to scroll node index.

cc/trees/property_tree_builder.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 "cc/trees/property_tree_builder.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <set>
@@ skipping 1140 matching lines @@
       main_thread_scrolling_reasons !=
       data_from_ancestor.main_thread_scrolling_reasons;
   bool requires_node =
       scroll_node_uninheritable_criteria ||
       (main_thread_scrolling_reasons !=
            MainThreadScrollingReason::kNotScrollingOnMain &&
        (has_different_main_thread_scrolling_reasons ||
         data_from_ancestor
             .scroll_tree_parent_created_by_uninheritable_criteria));
 
+  int node_id;
   if (!requires_node) {
-    data_for_children->scroll_tree_parent = parent_id;
+    node_id = parent_id;
+    data_for_children->scroll_tree_parent = node_id;
   } else {
     ScrollNode node;
     node.owning_layer_id = layer->id();
     node.scrollable = scrollable;
     node.main_thread_scrolling_reasons = main_thread_scrolling_reasons;
     node.contains_non_fast_scrollable_region =
         contains_non_fast_scrollable_region;
     gfx::Size clip_bounds;
     if (layer->scroll_clip_layer()) {
       clip_bounds = layer->scroll_clip_layer()->bounds();
@@ skipping 14 matching lines @@
 
     node.bounds = layer->bounds();
     node.offset_to_transform_parent = layer->offset_to_transform_parent();
     node.should_flatten = layer->should_flatten_transform_from_property_tree();
     node.user_scrollable_horizontal = layer->user_scrollable_horizontal();
     node.user_scrollable_vertical = layer->user_scrollable_vertical();
     node.element_id = layer->element_id();
     node.transform_id =
         data_for_children->transform_tree_parent->transform_tree_index();
 
-    data_for_children->scroll_tree_parent =
+    node_id =
         data_for_children->property_trees->scroll_tree.Insert(node, parent_id);
+    data_for_children->scroll_tree_parent = node_id;
     data_for_children->main_thread_scrolling_reasons =
         node.main_thread_scrolling_reasons;
     data_for_children->scroll_tree_parent_created_by_uninheritable_criteria =
         scroll_node_uninheritable_criteria;
     data_for_children->property_trees
-        ->layer_id_to_scroll_node_index[layer->id()] =
-        data_for_children->scroll_tree_parent;
+        ->layer_id_to_scroll_node_index[layer->id()] = node_id;
+    // For animation subsystem purposes, if this layer has a compositor element
+    // id, we build a map from that id to this scroll node.
+    if (layer->element_id()) {
+      data_for_children->property_trees
+          ->element_id_to_scroll_node_index[layer->element_id()] = node_id;
+    }
 
     if (node.scrollable) {
       data_for_children->property_trees->scroll_tree.SetBaseScrollOffset(
           layer->id(), layer->CurrentScrollOffset());
     }
   }
 
-  layer->SetScrollTreeIndex(data_for_children->scroll_tree_parent);
+  layer->SetScrollTreeIndex(node_id);
 }
 
 template <typename LayerType>
 void SetBackfaceVisibilityTransform(LayerType* layer,
                                     bool created_transform_node) {
   const bool is_at_boundary_of_3d_rendering_context =
       IsAtBoundaryOf3dRenderingContext(layer);
   if (layer->use_parent_backface_visibility()) {
     DCHECK(!is_at_boundary_of_3d_rendering_context);
     DCHECK(Parent(layer));
@@ skipping 315 matching lines @@
     color = SkColorSetA(color, 255);
   BuildPropertyTreesTopLevelInternal(
       root_layer, page_scale_layer, inner_viewport_scroll_layer,
       outer_viewport_scroll_layer, overscroll_elasticity_layer,
       elastic_overscroll, page_scale_factor, device_scale_factor, viewport,
       device_transform, property_trees, color);
   property_trees->ResetCachedData();
 }
 
 }  // namespace cc