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