Test readPixels on compressed textures

Bug: skia:9680
Change-Id: Ic31ec99b349a1b6585d06f36186b7e9d1d46048c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/265096
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
5 files changed