Implement 'scroll-behavior' parsing

Source/core/css/parser/BisonCSSParser-in.cpp

Index: Source/core/css/parser/BisonCSSParser-in.cpp
diff --git a/Source/core/css/parser/BisonCSSParser-in.cpp b/Source/core/css/parser/BisonCSSParser-in.cpp
index c73a4b5fc0345e2ea229f455a90b36218af6f37f..0ff4c425ffe7f23faa092f798bb2f1a7a3961bc5 100644
--- a/Source/core/css/parser/BisonCSSParser-in.cpp
+++ b/Source/core/css/parser/BisonCSSParser-in.cpp
@@ -575,6 +575,9 @@ static inline bool isValidKeywordPropertyAndValue(CSSPropertyID propertyId, int
         if (valueID == CSSValueNone || valueID == CSSValueBoth || valueID == CSSValueHorizontal || valueID == CSSValueVertical || valueID == CSSValueAuto)
             return true;
         break;
+    case CSSPropertyScrollBehavior: // instant | smooth
+        if (valueID == CSSValueInstant || valueID == CSSValueSmooth)
+            return RuntimeEnabledFeatures::cssomSmoothScrollEnabled();
     case CSSPropertySpeak: // none | normal | spell-out | digits | literal-punctuation | no-punctuation | inherit
         if (valueID == CSSValueNone || valueID == CSSValueNormal || valueID == CSSValueSpellOut || valueID == CSSValueDigits || valueID == CSSValueLiteralPunctuation || valueID == CSSValueNoPunctuation)
             return true;
@@ -867,6 +870,7 @@ static inline bool isKeywordPropertyID(CSSPropertyID propertyId)
     case CSSPropertyPointerEvents:
     case CSSPropertyPosition:
     case CSSPropertyResize:
+    case CSSPropertyScrollBehavior:
     case CSSPropertySpeak:
     case CSSPropertyTableLayout:
     case CSSPropertyTextAlignLast: