Use GetStyleRecalcParent for recalc root ancestors.

This ParentOrShadowHostNode() -> GetStyleRecalcParent() change was
missing in [1]. Caused many test failures with FlatTreeStyleRecalc
enabled.

[1] https://crrevs.com/d7eefe3ee4e1b35b57faf3060bed03ca2b1f73c3

Bug: 972752
Change-Id: Ife9858e7ab36f6dfbca0a423ffef953fedd6ffba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1841452Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703286}

third_party/blink/renderer/core/css/style_engine.cc

@@ -1746,8 +1746,8 @@ void StyleEngine::RecalcStyle() {
   SelectorFilterRootScope filter_scope(parent);
   root_element->RecalcStyle({});
 
-  for (ContainerNode* ancestor = root_element->ParentOrShadowHostNode();
-       ancestor; ancestor = ancestor->ParentOrShadowHostNode()) {
+  for (ContainerNode* ancestor = root_element->GetStyleRecalcParent(); ancestor;
+       ancestor = ancestor->GetStyleRecalcParent()) {
     if (auto* ancestor_element = DynamicTo<Element>(ancestor))
       ancestor_element->RecalcStyleForTraversalRootAncestor();
     ancestor->ClearChildNeedsStyleRecalc();