Handle nested position:sticky elements correctly (compositor)

cc/layers/layer.cc

 // Copyright 2010 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/layers/layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 564 matching lines @@
   SetSubtreePropertyChanged();
   PropertyTrees* property_trees = layer_tree_host_->property_trees();
   if (TransformNode* transform_node =
           property_trees->transform_tree.FindNodeFromOwningLayerId(id())) {
     DCHECK_EQ(transform_tree_index(), transform_node->id);
     transform_node->update_post_local_transform(position, transform_origin());
     if (transform_node->sticky_position_constraint_id >= 0) {
       StickyPositionNodeData* sticky_data =
           property_trees->transform_tree.StickyPositionData(
               transform_tree_index());
+      // TODO(smcgruer): Pass main thread sticky-shifting offsets of
+      // non-promoted ancestors, or promote all ancestor sticky elements.
+      // See http://crbug.com/702229
       sticky_data->main_thread_offset =
           position.OffsetFromOrigin() -
           sticky_data->constraints.parent_relative_sticky_box_offset
               .OffsetFromOrigin();
     }
     transform_node->needs_local_transform_update = true;
     transform_node->transform_changed = true;
     layer_tree_host_->property_trees()->transform_tree.set_needs_update(true);
     SetNeedsCommitNoRebuild();
     return;
@@ skipping 884 matching lines @@
       ->num_copy_requests_in_subtree;
 }
 
 gfx::Transform Layer::screen_space_transform() const {
   DCHECK_NE(transform_tree_index_, TransformTree::kInvalidNodeId);
   return draw_property_utils::ScreenSpaceTransform(
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 }  // namespace cc