def start_workunit(self, workunit):
    """Implementation of Reporter callback."""
    if not self.is_under_main_root(workunit):
      return

    label_format = self._get_label_format(workunit)

    if label_format == LabelFormat.FULL:
      if not WorkUnitLabel.SUPPRESS_LABEL in workunit.labels:
        self._emit_indented_workunit_label(workunit)
      # Start output on a new line.
      tool_output_format = self._get_tool_output_format(workunit)
      if tool_output_format == ToolOutputFormat.INDENT:
        self.emit(self._prefix(workunit, '\n'))
      elif tool_output_format == ToolOutputFormat.UNINDENTED:
        self.emit('\n')
    elif label_format == LabelFormat.DOT:
      self.emit('.')

    self.flush()
Implementation of Reporter callback.