Replace compile flag with runtime check for text-underline-position

Source/core/page/RuntimeCSSEnabled.cpp

 /*
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 53 matching lines @@
         CSSPropertyShapePadding,
         CSSPropertyShapeImageThreshold,
         CSSPropertyShapeInside,
         CSSPropertyShapeOutside,
     };
     setCSSPropertiesEnabled(shapeProperties, WTF_ARRAY_LENGTH(shapeProperties), RuntimeEnabledFeatures::cssShapesEnabled());
     CSSPropertyID css3TextDecorationProperties[] = {
         CSSPropertyTextDecorationColor,
         CSSPropertyTextDecorationLine,
         CSSPropertyTextDecorationStyle,
+        CSSPropertyTextUnderlinePosition,
     };
     setCSSPropertiesEnabled(css3TextDecorationProperties, WTF_ARRAY_LENGTH(css3TextDecorationProperties), RuntimeEnabledFeatures::css3TextDecorationsEnabled());
     CSSPropertyID css3TextProperties[] = {
         CSSPropertyTextAlignLast,
         CSSPropertyTextJustify,
     };
     setCSSPropertiesEnabled(css3TextProperties, WTF_ARRAY_LENGTH(css3TextProperties), RuntimeEnabledFeatures::css3TextEnabled());
     CSSPropertyID cssGridLayoutProperties[] = {
         CSSPropertyGridAutoColumns,
         CSSPropertyGridAutoRows,
@@ skipping 79 matching lines @@
 void RuntimeCSSEnabled::filterEnabledCSSPropertiesIntoVector(const CSSPropertyID* properties, size_t propertyCount, Vector<CSSPropertyID>& outVector)
 {
     for (unsigned i = 0; i < propertyCount; i++) {
         CSSPropertyID property = properties[i];
         if (RuntimeCSSEnabled::isCSSPropertyEnabled(property))
             outVector.append(property);
     }
 }
 
 } // namespace WebCore