Samples: simplify Sample::Event

Change-Id: I1daaa9dcf56812bfd29dab64ee04dae63c2660e1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/225545
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
30 files changed