code: func (wc *WhisperClient) MarkTrustedPeer(ctx *Context, enode string) error {
  	return wc.client.MarkTrustedPeer(ctx.context, enode)
  }
docs: // Marks specific peer trusted, which will allow it to send historic (expired) messages.
  // Note This function is not adding new nodes, the node needs to exists as a peer.