Cancels the current request. This will close any open input or output streams and terminate any async requests. Users should normally pass NS_BINDING_ABORTED, although other errors may also be passed. The error passed in will become the value of the status attribute.
Implementations must not send any notifications (e.g. via nsIRequestObserver) synchronously from this function. Similarly, removal from the load group (if any) must also happen asynchronously.
Requests that use nsIStreamListener must not call onDataAvailable anymore after cancel has been called.