Generate enum/getters/setters/mappings for user-modify.

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 2672 matching lines @@
       name: "-webkit-transform-origin-z",
       api_class: true,
       api_methods: ["parseSingleValue"],
       converter: "ConvertComputedLength<float>",
       interpolable: true,
     },
     "-webkit-user-drag",
     {
       name: "-webkit-user-modify",
       inherited: true,
-      field_template: "storage_only",
-      type_name: "EUserModify",
-      default_value: "EUserModify::kReadOnly",
-      field_size: 2,
+      field_template: "keyword",
+      keywords: ["read-only", "read-write", "read-write-plaintext-only"],
+      default_value: "read-only",
       field_group: "rare-inherited",
     },
     {
       name: "user-select",
       inherited: true,
       field_template: "keyword",
       keywords: ["none", "text", "all"],
       default_value: "text",
       field_group: "rare-inherited",
     },
@@ skipping 821 matching lines @@
     {
       name: "-webkit-transition-timing-function",
       alias_for: "transition-timing-function",
     },
     {
       name: "-webkit-user-select",
       alias_for: "user-select",
     },
   ],
 }