Disable async readback from protected memory

Reading back pixel values from protected memory into cpu memory is
not allowed. This CL adds early returns so they are not attempted.

Bug: skia:9016, fuchsia:38648
Change-Id: Icc0b51a62e87b7aebd0e7cb2a061fea084e7f754
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/251000
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
2 files changed