public enum TrackType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable  

//spatial or non-spatial?
if (streamLayer.TrackType == TrackType.AttributeOnly)
{
  //this is a non-spatial stream layer
}
else
{
  //this must be a spatial stream layer
}

var trackType = streamLayer.TrackType;
switch(trackType)
{
  //TODO deal with tracktype
  case TrackType.None:
  case TrackType.AttributeOnly:
  case TrackType.Spatial:
    break;
}

//The layer must be track aware and spatial
if (streamLayer.TrackType != TrackType.Spatial)
  return;
//Must be on QueuedTask
//get the CIM Definition
var def = streamLayer.GetDefinition() as CIMFeatureLayer;
//set the number of previous observations, 
def.PreviousObservationsCount = (int)streamLayer.GetExpirationMaxCount() - 1;
//set show previous observations and track lines to true
def.ShowPreviousObservations = true;
def.ShowTracks = true;
//commit the changes
streamLayer.SetDefinition(def);