Implemented the CSSPropertyAPI for the font-family property.

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 318 matching lines @@
       custom_value: true,
       field_type_path: "platform/text/TextDirection",
       inherited: true,
       initial_keyword: "ltr",
       field_template: "keyword",
       keywords: ["ltr", "rtl"],
       priority: "High",
     },
     {
       name: "font-family",
+      api_class: true,
+      api_methods: ["parseSingleValue"],
       converter: "convertFontFamily",
       font: true,
       inherited: true,
       name_for_methods: "FamilyDescription",
       priority: "High",
       type_name: "FontDescription::FamilyDescription",
     },
     {
       name: "font-kerning",
       font: true,
@@ skipping 2757 matching lines @@
     {
       name: "-webkit-transition-timing-function",
       alias_for: "transition-timing-function",
     },
     {
       name: "-webkit-user-select",
       alias_for: "user-select",
     },
   ],
 }