tools/sk_app: fWindowContext is unique_ptr<>

Change-Id: I828f298e336da22756588d981481c76b890af2ee
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/231648
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
28 files changed