Merge "Revert of Make A8 readback work in more cases and improve testing. (patchset #5 id:70001 of https://codereview.chromium.org/1584563002/ )" into master-skia

https://skia.googlesource.com/skia/+/23e566664b85472766c921cd2f5615c846919934

Change-Id: Ibef674f47944181cddb0b507d65cfdb36b3ab110