code: func printError(err error, options *gbuild.Options, browserErrors *bytes.Buffer) {
  	e := sprintError(err)
  	options.PrintError("%s\n", e)
  	if browserErrors != nil {
  		fmt.Fprintln(browserErrors, `console.error("`+template.JSEscapeString(e)+`");`)
  	}
  }
docs: // printError prints err to Stderr with options. If browserErrors is non-nil, errors are also written for presentation in browser.