Revert of small cleanup of GrAtlas (patchset #2 id:20001 of https://codereview.chromium.org/1142263002/)

Reason for revert:
Broke compile on Linux

Original issue's description:
> small cleanup of GrAtlas
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/d706f11b6e3f4398ab93b23458a7599ee324be2c

TBR=robertphillips@google.com,joshualitt@google.com,jvanverth@google.com,joshualitt@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1142273002
4 files changed