mDNSRequest->Cancel();
mDNSRequest->Cancel(NS_ERROR_ABORT);
PendingPACQuery::Complete(nsresult status, const nsCString &pacString){  if (!mCallback)    return;  mCallback->OnQueryComplete(status, pacString);  mCallback = nsnull;  if (mDNSRequest) {    mDNSRequest->Cancel();    mDNSRequest = nsnull;  }}