[css-pseudo] Let ListMarker::IsMarkerImage reject non-normal markers

ListMarker::IsMarkerImage was only checking the 'list-style-image' of
the list item. However, even if its value is an image, if the ::marker
has e.g. 'content: "foo"', then that takes precedence and the marker
won't be an image.

This patch makes it return true only if 'content' is 'normal'.

Most callers were already checking 'content' independently so there
shouldn't be much difference in practice, only in LayoutTreeAsText's
MarkerTextForListItem and AXLayoutObject's TextAlternative.

BUG=457718

Change-Id: If74ed3e847d9989b33a99de62306fd2cbc223ca6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107631
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#777319}

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

@@ -264,4 +264,10 @@ LayoutObject* ListMarker::SymbolMarkerLayoutText(
   return marker.SlowFirstChild();
 }
 
+bool ListMarker::IsMarkerImage(const LayoutObject& marker) const {
+  DCHECK_EQ(Get(&marker), this);
+  return marker.StyleRef().ContentBehavesAsNormal() &&
+         ListItem(marker)->StyleRef().GeneratesMarkerImage();
+}
+
 }  // namespace blink

third_party/blink/renderer/core/layout/list_marker.h

@@ -30,10 +30,7 @@ class CORE_EXPORT ListMarker {
   // Marker text with suffix, e.g. "1. ", for use in accessibility.
   String TextAlternative(const LayoutObject&) const;
 
-  bool IsMarkerImage(const LayoutObject& marker) const {
-    DCHECK_EQ(Get(&marker), this);
-    return ListItem(marker)->StyleRef().GeneratesMarkerImage();
-  }
+  bool IsMarkerImage(const LayoutObject&) const;
 
   void UpdateMarkerTextIfNeeded(LayoutObject& marker) {
     DCHECK_EQ(Get(&marker), this);