Removed CSSDisplayContents runtime flag.

In stable since M65.

Bug: 657748
Change-Id: I25bd7ae44e3084b3a198eff6bad811118a460d52
Reviewed-on: https://chromium-review.googlesource.com/1156548
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579437}

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

@@ -601,8 +601,7 @@ bool CSSParserFastPaths::IsValidKeywordPropertyAndValue(
              value_id == CSSValueWebkitFlex ||
              value_id == CSSValueWebkitInlineFlex || value_id == CSSValueNone ||
              value_id == CSSValueGrid || value_id == CSSValueInlineGrid ||
-             (RuntimeEnabledFeatures::CSSDisplayContentsEnabled() &&
-              value_id == CSSValueContents);
+             value_id == CSSValueContents;
     case CSSPropertyDominantBaseline:
       return value_id == CSSValueAuto || value_id == CSSValueAlphabetic ||
              value_id == CSSValueMiddle ||

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -254,10 +254,6 @@
       name: "CSSBackdropFilter",
       status: "experimental",
     },
-    {
-      name: "CSSDisplayContents",
-      status: "stable",
-    },
     {
       name: "CSSEnvironmentVariables",
       status: "stable",