The URLRequest class captures all of the information in a single HTTP request.
URLRequest objects are passed to the load() methods of the
Loader, URLStream, and URLLoader classes, and to other loading operations,
to initiate URL downloads.
They are also passed to the upload() and download() methods
of the FileReference class.
Creates a URLRequest object.
If System.useCodePage is true,
the request is encoded using the system code page, rather than Unicode.
If System.useCodePage is false,
the request is encoded using Unicode, rather than the system code page.
url:String (default = null) — The URL to be requested.
You can set the URL later by using the url property.