[Plot] Complete specs related to stacked mode

Add specs for SubPlot, which was introduced to support
presenting multiple plot areas within a single plot
view (stacked plots, WTD-625.)

platform/features/plot/src/SubPlot.js

@@ -127,6 +127,11 @@ define(
                 updateTicks();
             }
 
+            // Start with the right initial drawing bounds,
+            // tick marks
+            updateDrawingBounds();
+            updateTicks();
+
             return {
                 getTelemetryObjects: function () {
                     return telemetryObjects;