1. @DomName('FormData.appendBlob')
  2. @DocsEditable()
void appendBlob(String name, Blob value, [ String filename ])

Source 

@DomName('FormData.appendBlob')
@DocsEditable()
void appendBlob(String name, Blob value, [String filename]) =>
    _blink.BlinkFormData.instance
        .append_Callback_3_(this, name, value, filename);