Remove HTMLSlotElement's dead member fields

There members are no longer necessary after Incremental Shadow DOM is shipped.

Bug: 887827
Change-Id: Ic1e389f248de401f367d031f5ae13242e1fe6dca
Reviewed-on: https://chromium-review.googlesource.com/1249474Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594985}

third_party/blink/renderer/core/html/html_slot_element.cc

@@ -617,9 +617,6 @@ int HTMLSlotElement::tabIndex() const {
 void HTMLSlotElement::Trace(blink::Visitor* visitor) {
   visitor->Trace(assigned_nodes_);
   visitor->Trace(flat_tree_children_);
-  visitor->Trace(distributed_nodes_);
-  visitor->Trace(old_distributed_nodes_);
-  visitor->Trace(distributed_indices_);
   visitor->Trace(assigned_nodes_candidates_);
   HTMLElement::Trace(visitor);
 }

third_party/blink/renderer/core/html/html_slot_element.h

@@ -147,14 +147,8 @@ class CORE_EXPORT HTMLSlotElement final : public HTMLElement {
 
   HeapHashSet<Member<Node>> assigned_nodes_candidates_;
 
-  // For IncrementalShadowDOM
   HeapVector<Member<Node>> flat_tree_children_;
 
-  // For Non-IncrmentalShadowDOM. IncremntalShadowDOM never use these members.
-  HeapVector<Member<Node>> distributed_nodes_;
-  HeapVector<Member<Node>> old_distributed_nodes_;
-  HeapHashMap<Member<const Node>, wtf_size_t> distributed_indices_;
-
   // TODO(hayato): Move this to more appropriate directory (e.g. platform/wtf)
   // if there are more than one usages.
   template <typename Container, typename LCSTable, typename BacktrackTable>