exit demo on escape key

Change-Id: Ia7c4ba28900d98eb2559ae39917f001b98a438c4
Reviewed-on: https://skia-review.googlesource.com/c/eskia/+/198527
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed