Generate a summary of the warnings and errors.

    Returns:
      The generated HTML as a string.

def _GenerateSummary(self):
    """Generate a summary of the warnings and errors.

    Returns:
      The generated HTML as a string.
    """
    items = []
    if self._notices:
      items.append('notices: %d' % self._notice_count)
    if self._dataset_errors:
      items.append('errors: %d' % self._error_count)
    if self._dataset_warnings:
      items.append('warnings: %d' % self._warning_count)

    if items:
      return '<p><span class="fail">%s</span></p>' % '<br>'.join(items)
    else:
      return '<p><span class="pass">feeds merged successfully</span></p>'