Extract only the operating system type from the active histogram.

def GetReportData(self, get_report_args, token):
    """Extract only the operating system type from the active histogram."""
    report = rdf_report_plugins.ApiReportData(
        representation_type=rdf_report_plugins.ApiReportData.RepresentationType
        .PIE_CHART)

    graph_series = client_report_utils.FetchMostRecentGraphSeries(
        get_report_args.client_label,
        rdf_stats.ClientGraphSeries.ReportType.OS_TYPE,
        token=token)
    if graph_series is not None:
      for graph in graph_series.graphs:
        # Find the correct graph and merge the OS categories together
        if "%s day" % self.__class__.ACTIVE_DAYS in graph.title:
          for sample in graph:
            report.pie_chart.data.Append(
                rdf_report_plugins.ApiReportDataPoint1D(
                    label=sample.label, x=sample.y_value))
          break

    report.pie_chart.data = sorted(
        report.pie_chart.data, key=lambda point: point.label)

    return report