[LayoutNG] Avoid copying NGOutOfFlowPositionedDescendant

Bug: 635619
Change-Id: I5f2992f95f755e56c34ce5a89c5185ae31b6537f
Reviewed-on: https://chromium-review.googlesource.com/c/1333010Reviewed-by: Aleks Totic <atotic@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607517}

third_party/blink/renderer/core/layout/ng/layout_ng_block_flow.cc

@@ -65,7 +65,7 @@ void LayoutNGBlockFlow::UpdateBlockLayout(bool relayout_children) {
   scoped_refptr<NGLayoutResult> result =
       NGBlockNode(this).Layout(constraint_space);
 
-  for (NGOutOfFlowPositionedDescendant descendant :
+  for (const NGOutOfFlowPositionedDescendant& descendant :
        result->OutOfFlowPositionedDescendants())
     descendant.node.UseOldOutOfFlowPositioning();
 

third_party/blink/renderer/core/layout/ng/ng_block_node.cc

@@ -977,7 +977,7 @@ void NGBlockNode::UpdateShapeOutsideInfoIfNeeded(
       percentage_resolution_inline_size);
 }
 
-void NGBlockNode::UseOldOutOfFlowPositioning() {
+void NGBlockNode::UseOldOutOfFlowPositioning() const {
   DCHECK(box_->IsOutOfFlowPositioned());
   box_->ContainingBlock()->InsertPositionedObject(box_);
 }

third_party/blink/renderer/core/layout/ng/ng_block_node.h

@@ -87,7 +87,7 @@ class CORE_EXPORT NGBlockNode final : public NGLayoutInputNode {
 
   // Called if this is an out-of-flow block which needs to be
   // positioned with legacy layout.
-  void UseOldOutOfFlowPositioning();
+  void UseOldOutOfFlowPositioning() const;
 
   // Save static position for legacy AbsPos layout.
   void SaveStaticOffsetForLegacy(const NGLogicalOffset&,