[graphite] Expand shader precompilation placeholder

Bug: skia:12466
Change-Id: If633ce39c8f45b1ee3c042b5b72d7e0f95ca5c19
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/459597
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
9 files changed