[css-pseudo] Remove CSSMarkerPseudoElement flag

It has been enabled by default since M86.

Bug: 457718
Change-Id: I89f115d310d5e0a3f83ad7cdcbabe4f52d9c2d72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593377
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837424}

third_party/blink/renderer/core/css/parser/css_selector_parser.cc

@@ -638,11 +638,8 @@ std::unique_ptr<CSSParserSelector> CSSSelectorParser::ConsumePseudo(
         context_->Count(WebFeature::kHasBeforeOrAfterPseudoElement);
         break;
       case CSSSelector::kPseudoMarker:
-        if (context_->Mode() != kUASheetMode) {
+        if (context_->Mode() != kUASheetMode)
           context_->Count(WebFeature::kHasMarkerPseudoElement);
-          if (!RuntimeEnabledFeatures::CSSMarkerPseudoElementEnabled())
-            return nullptr;
-        }
         break;
       default:
         break;

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

@@ -99,7 +99,7 @@ bool PseudoElement::IsWebExposed(PseudoId pseudo_id, const Node* parent) {
     case kPseudoIdMarker:
       if (parent && parent->IsPseudoElement())
         return RuntimeEnabledFeatures::CSSMarkerNestedPseudoElementEnabled();
-      return RuntimeEnabledFeatures::CSSMarkerPseudoElementEnabled();
+      return true;
     default:
       return true;
   }

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -554,11 +554,6 @@
       name: "CSSMarkerNestedPseudoElement",
       status: "experimental",
     },
-    {
-      name: "CSSMarkerPseudoElement",
-      status: "stable",
-      implied_by: ["CSSMarkerNestedPseudoElement"],
-    },
     // Enables dependency support for the MatchedPropertiesCache.
     {
       name: "CSSMatchedPropertiesCacheDependencies",