[Squad] Do not ask for cached pseudo element style.

The goal is to remove the need for a pseudo style cache for pseudo
elements which have a PseudoElement on which we store a ComputedStyle
and a LayoutObject.

This CL removes an extra call to PseudoStyle() which would access the
pseudo style cache to re-retrieve the ComputedStyle(). Instead use
GetNonAttachedStyle() which would be set by the RecalcStyle() call for
re-attachment, or to null if the PseudoElement is no longer needed.

Bug: 836126
Change-Id: Ide807be656843fcbfad35fce7b2f3ed1c858a0f6
Reviewed-on: https://chromium-review.googlesource.com/1096761Reviewed-by: Anders Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566384}

third_party/blink/renderer/core/dom/element.cc

@@ -2251,8 +2251,11 @@ StyleRecalcChange Element::RecalcOwnStyle(StyleRecalcChange change) {
   scoped_refptr<ComputedStyle> new_style = PropagateInheritedProperties(change);
   if (!new_style)
     new_style = StyleForLayoutObject();
-  if (!new_style)
+  if (!new_style) {
+    DCHECK(IsPseudoElement());
+    SetNeedsReattachLayoutTree();
     return kReattach;
+  }
 
   StyleRecalcChange local_change =
       ComputedStyle::StylePropagationDiff(old_style.get(), new_style.get());
@@ -3851,18 +3854,16 @@ void Element::UpdatePseudoElement(PseudoId pseudo_id,
     if (element->NeedsStyleRecalc())
       MutableComputedStyle()->RemoveCachedPseudoStyle(pseudo_id);
 
-    // PseudoElement styles hang off their parent element's style so if we
-    // needed a style recalc we should Force one on the pseudo.
-    element->RecalcStyle(change == kUpdatePseudoElements ? kForce : change);
-
-    // Wait until our parent is not displayed or
-    // PseudoElementLayoutObjectIsNeeded is false, otherwise we could
-    // continuously create and destroy PseudoElements when
-    // LayoutObject::IsChildAllowed on our parent returns false for the
-    // PseudoElement's GetLayoutObject for each style recalc.
-    if (!CanGeneratePseudoElement(pseudo_id) ||
-        !PseudoElementLayoutObjectIsNeeded(
-            PseudoStyle(PseudoStyleRequest(pseudo_id))))
+    bool remove_pseudo = !CanGeneratePseudoElement(pseudo_id);
+    if (!remove_pseudo) {
+      // PseudoElement styles hang off their parent element's style so if we
+      // needed a style recalc we should Force one on the pseudo.
+      element->RecalcStyle(change == kUpdatePseudoElements ? kForce : change);
+      remove_pseudo =
+          element->NeedsReattachLayoutTree() &&
+          !PseudoElementLayoutObjectIsNeeded(element->GetNonAttachedStyle());
+    }
+    if (remove_pseudo)
       GetElementRareData()->SetPseudoElement(pseudo_id, nullptr);
   } else if (pseudo_id == kPseudoIdFirstLetter && element &&
              change >= kUpdatePseudoElements &&