code: function EventContainer() {
      this.guid_ = tr.b.GUID.allocate();
      this.important = true;
      this.bounds_ = new tr.b.Range();
    }
docs: EventContainer is a base class for any class in the trace model that
  contains child events or child EventContainers.
  
  For all EventContainers, updateBounds() must be called after modifying the
  container's events if an up-to-date bounds is expected.
  
  @constructor