Make TextDecoration an enum class.

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

 {
 // This file specifies fields in ComputedStyle that we would like to
 // generate, but are not CSS properties.
 
   parameters: {
     // If the field has_custom_compare_and_copy, then it does not appear in
     // ComputedStyle::operator== and ComputedStyle::CopyNonInheritedFromCached.
     has_custom_compare_and_copy: {
       default: false,
     },
@@ skipping 190 matching lines @@
       field_template: "storage_only",
       field_type_path: "core/css/StyleColor",
       default_value: "Color::kTransparent",
       field_group: "background",
     },
     {
       name: "TextDecoration",
       field_template: "storage_only",
       type_name: "TextDecoration",
       field_size: 4,
-      default_value: "kTextDecorationNone",
+      default_value: "TextDecoration::kNone",
       field_group: "visual",
     },
     {
       name: "HasAutoClip",
       field_template: "storage_only",
       type_name: "bool",
       field_size: 1,
       default_value: "true",
       field_group: "visual",
     },
   ],
 }