Revert of Remove SkPictureFlat.h include from SkDrawCommands.h (patchset #3 id:40001 of https://codereview.chromium.org/912403004/)

Reason for revert:
Erm - Chrome.

Original issue's description:
> Remove SkPictureFlat.h include from SkDrawCommands.h
>
> This cannot land until https://codereview.chromium.org/909353004/ (Prepare SkiaBenchmarkingExtensionTest for upcoming Skia changes) lands in Chromium
>
> Committed: https://skia.googlesource.com/skia/+/5a4c233a3657d12d836de388b41e30405b4ab976
>
> Committed: https://skia.googlesource.com/skia/+/fa3a83d0fe53907e618346d3f1c17a95da1a9d22

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

Review URL: https://codereview.chromium.org/923753002
6 files changed