Make TextUnderlinePosition an enum class.

third_party/WebKit/Source/core/css/CSSProperties.json5

 {
 // This file specifies all the CSS properties we support and the necessary
 // information for our code generation. The various supported arguments
 // are described below with example usage
 
   parameters: {
     // - alias_for: "other-property"
     // Properties specifying alias_for should be virtually identical to the
     // properties they alias. Minor parsing differences are allowed as long as
     // the CSSValues created are of the same format of the aliased property.
@@ skipping 2130 matching lines @@
       keywords: ["capitalize", "uppercase", "lowercase", "none"],
     },
     {
       name: "text-underline-position",
       api_class: true,
       api_methods: ["parseSingleValue"],
       inherited: true,
       runtime_flag: "CSS3TextDecorations",
       field_template: "storage_only",
       type_name: "TextUnderlinePosition",
-      default_value: "kTextUnderlinePositionAuto",
+      default_value: "TextUnderlinePosition::kAuto",
       field_size: 1,
       field_group: "rare-inherited",
     },
     {
       name: "top",
       api_class: "CSSPropertyAPIMargin",
       api_methods: ["parseSingleValue"],
       converter: "ConvertLengthOrAuto",
       interpolable: true,
       keywords: ["auto"],
@@ skipping 1363 matching lines @@
     {
       name: "-webkit-transition-timing-function",
       alias_for: "transition-timing-function",
     },
     {
       name: "-webkit-user-select",
       alias_for: "user-select",
     },
   ],
 }