Revert of Remove SkPictureFlat.h include from SkDrawCommands.h (patchset #2 id:20001 of https://codereview.chromium.org/912403004/)

Reason for revert:
Chrome

Original issue's description:
> Remove SkPictureFlat.h include from SkDrawCommands.h
>
> Committed: https://skia.googlesource.com/skia/+/5a4c233a3657d12d836de388b41e30405b4ab976

TBR=reed@google.com,fmalita@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/917933002
6 files changed