Refer to screenshot. I simply added a setEditable(false) to HelloDatePicker.

A related issue (which I can file separately or just note here for now) is that due to RT-29824 I have backed out my previous change, and now non-editable ComboBox should show prompt text. I've got the backout in my local repo, but I have not applied it to DatePicker (but this is the reason why I stumbled on this bug).