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);