[css-pseudo] Don't propagate style to children of normal markers

In r720875 I changed the pseudo type of the style used for markers with
'content: normal' from kPseudoIdNone to kPseudoIdMarker. This had the
side effect that they started to propagate style to its children,
producing a 90.6%-99.9% performance regression in the
flexbox_with_list_item test.

This patch prevents that style propagationg for normal markers, fixing
the perf regression. Markers with 'content' different than 'normal' are
still propagated since it's necessary in that case.

Bug: 1030884, 457718
Change-Id: Ia8341b605366ebdfd117cf569d030b38862348dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1953723Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#722421}

third_party/blink/renderer/core/layout/layout_object.cc

@@ -2489,7 +2489,13 @@ void LayoutObject::PropagateStyleToAnonymousChildren() {
     child->SetStyle(std::move(new_style));
   }
 
-  if (StyleRef().StyleType() == kPseudoIdNone)
+  PseudoId pseudo_id = StyleRef().StyleType();
+  if (pseudo_id == kPseudoIdNone)
+    return;
+
+  // Don't propagate style from markers with 'content: normal' because it's not
+  // needed and it would be slow.
+  if (pseudo_id == kPseudoIdMarker && !StyleRef().GetContentData())
     return;
 
   // Propagate style from pseudo elements to generated content. We skip children