Clean up promises in example.html and extra.html

Change-Id: I8b8500b4cda3d9b190bd8553ac5a68aef7b9007d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/291338
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
2 files changed