Revert of Don't flush on read/write pixels unless necessary (patchset #2 id:20001 of https://codereview.chromium.org/586073002/)

Reason for revert:
Breaking the tree

Original issue's description:
> Don't flush on read/write pixels unless necessary
>
> BUG=skia:2889
>
> Committed: https://skia.googlesource.com/skia/+/150723b9298772a5096bec7acd2999c5c9d66239

R=robertphillips@google.com
TBR=robertphillips@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:2889

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/594543004
5 files changed