def onload_event
      @onload_event ||= begin
                          ts = @events.select { |event|
                            event.is_a?(LoadEventFired)
                          }.slice(0,1).map(&:timestamp).first
                          ts ? (ts - start_time).round(3) : nil
                        end
    end
def onload_event
      @onload_event ||= begin
                          ts = @events.select { |event|
                            event.is_a?(LoadEventFired)
                          }.slice(0,1).map(&:timestamp).first
                          ts ? (ts - start_time).round(3) : nil
                        end
    end
The number of seconds *after* start_time that the OnLoad event fired