Generate getters/setters for subtree_is_sticky.

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 466 matching lines @@
       type_name: "bool",
       default_value: "false",
       field_size: 1,
       field_group: "rare-inherited",
     },
     // Though position: sticky is not itself an inherited property, being a
     // descendent of a sticky element changes some document lifecycle logic.
     {
       name: "SubtreeIsSticky",
       inherited: true,
-      field_template: "storage_only",
+      field_template: "primitive",
       type_name: "bool",
       default_value: "false",
       field_size: 1,
       field_group: "rare-inherited",
     },
     {
       name: "HyphenationLimitBefore",
       inherited: true,
       field_template: "storage_only",
       type_name: "short",
@@ skipping 37 matching lines @@
       name: "Variables",
       inherited: true,
       field_template: "storage_only",
       field_type_path: "core/style/StyleInheritedVariables",
       default_value: "nullptr",
       wrapper_pointer_name: "RefPtr",
       field_group: "rare-inherited",
     },
   ],
 }