Add a runtime flag for the column-fill property.

Source/core/css/parser/CSSParserFastPaths.cpp

Index: Source/core/css/parser/CSSParserFastPaths.cpp
diff --git a/Source/core/css/parser/CSSParserFastPaths.cpp b/Source/core/css/parser/CSSParserFastPaths.cpp
index 846fd07242611f240e33c64cd22ae262844bf3a8..27c80debb74f7f175f3f83c5545235770274980b 100644
--- a/Source/core/css/parser/CSSParserFastPaths.cpp
+++ b/Source/core/css/parser/CSSParserFastPaths.cpp
@@ -308,7 +308,7 @@ bool CSSParserFastPaths::isValidKeywordPropertyAndValue(CSSPropertyID propertyId
     case CSSPropertyWebkitBoxPack:
         return valueID == CSSValueStart || valueID == CSSValueEnd || valueID == CSSValueCenter || valueID == CSSValueJustify;
     case CSSPropertyColumnFill:
-        ASSERT(RuntimeEnabledFeatures::regionBasedColumnsEnabled());
+        ASSERT(RuntimeEnabledFeatures::unprefixMulticolEnabled());
         return valueID == CSSValueAuto || valueID == CSSValueBalance;
     case CSSPropertyAlignItems:
         // FIXME: Per CSS alignment, this property should accept the same arguments as 'justify-self' so we should share its parsing code.