[graphite] Update viewer's flag handling

Bug: b/362718561
Change-Id: Icc266cce7742f22a39ada681d952d22ac902728c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/896977
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
11 files changed