Hi Bob,
We can achieve your requirement by making the following changes.
For Stack Layout: In your Sample, the layout options for the children in the stack layout are not defined and we have defined the layout options as fill and expand to make the chart visible.
For Grid Layout: In your sample, too many row definitions are used to fit into the view cell and we have reduced the row definitions to make the chart visible.
We have modified the sample and it can be downloaded from the below location.
Regards,
Jaikrishna C