Remove one use of ScrollNode's owning_layer_id for StickyPositionOffset

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 334 matching lines @@
   bool all_are_invertible = dest_to_source.GetInverse(&source_to_dest);
   transform->PreconcatTransform(source_to_dest);
   return all_are_invertible;
 }
 
 gfx::Vector2dF StickyPositionOffset(TransformTree* tree, TransformNode* node) {
   if (node->sticky_position_constraint_id == -1)
     return gfx::Vector2dF();
   StickyPositionNodeData* sticky_data = tree->StickyPositionData(node->id);
   const LayerStickyPositionConstraint& constraint = sticky_data->constraints;
+  auto& property_trees = *tree->property_trees();
   ScrollNode* scroll_node =
-      tree->property_trees()->scroll_tree.Node(sticky_data->scroll_ancestor);
-  gfx::ScrollOffset scroll_offset =
-      tree->property_trees()->scroll_tree.current_scroll_offset(
-          scroll_node->owning_layer_id);
+      property_trees.scroll_tree.Node(sticky_data->scroll_ancestor);
+  TransformNode* transform_node =
+      property_trees.transform_tree.Node(scroll_node->transform_id);
+  const auto& scroll_offset = transform_node->scroll_offset;
+  DCHECK(property_trees.scroll_tree.current_scroll_offset(

[chrishtr, 2017/05/12 22:11:20]

Add a note that this can be removed later, and is just here
to ensure correctness?

[enne (OOO), 2017/05/12 22:15:28]

Can you DCHECK_EQ this?

+             scroll_node->owning_layer_id) == scroll_offset);
   gfx::PointF scroll_position(scroll_offset.x(), scroll_offset.y());
-  TransformNode* scroll_ancestor_transform_node =
-      tree->Node(scroll_node->transform_id);
-  if (scroll_ancestor_transform_node->scrolls) {
+  if (transform_node->scrolls) {
     // The scroll position does not include snapping which shifts the scroll
     // offset to align to a pixel boundary, we need to manually include it here.
     // In this case, snapping is caused by a scroll.
-    scroll_position -= scroll_ancestor_transform_node->snap_amount;
+    scroll_position -= transform_node->snap_amount;
   }
 
   gfx::RectF clip(
       scroll_position,
-      gfx::SizeF(tree->property_trees()->scroll_tree.scroll_clip_layer_bounds(
+      gfx::SizeF(property_trees.scroll_tree.scroll_clip_layer_bounds(
           scroll_node->id)));
   gfx::Vector2dF layer_offset(sticky_data->main_thread_offset);
 
   gfx::Vector2dF ancestor_sticky_box_offset;
   if (sticky_data->nearest_node_shifting_sticky_box !=
       TransformTree::kInvalidNodeId) {
     ancestor_sticky_box_offset =
         tree->StickyPositionData(sticky_data->nearest_node_shifting_sticky_box)
             ->total_sticky_box_sticky_offset;
   }
@@ skipping 1737 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