function IdlInterfaceMember(obj)
{
    /**
     * obj is an object produced by the WebIDLParser.js "ifMember" production.
     * We just forward all properties to this object without modification,
     * except for special extAttrs handling.
     */
    for (var k in obj.toJSON())
    {
        this[k] = obj[k];
    }
    if (!("extAttrs" in this))
    {
        this.extAttrs = [];
    }

    this.isUnforgeable = this.has_extended_attribute("LegacyUnforgeable");
    this.isUnscopable = this.has_extended_attribute("Unscopable");
}
Implementation of
https://webidl.spec.whatwg.org/#default-tojson-operation
for testing purposes.

Collects the IDL types of the attributes that meet the criteria
for inclusion in the default toJSON operation for easy
comparison with actual value