Move prepareForExternalIO implementation from GrContext to GrDrawingManager

Move prepareForExternalIO implementation from GrContext to GrDrawingManager
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2324473002

Committed: https://skia.googlesource.com/skia/+/6a2b1941c1da272f704439e417f212932eed2004

[bsalomon, 2016-09-07 18:24:08]

Description was changed from

==========
Move prepareForExternalIO implementation from GrContext to GrDrawingManager
==========

to

==========
Move prepareForExternalIO implementation from GrContext to GrDrawingManager
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2324473002
==========

[bsalomon, 2016-09-07 18:25:29]

bsalomon@google.com changed reviewers:
+ robertphillips@google.com

[bsalomon, 2016-09-07 18:25:29]

I want to hook this in GrDM for better control of when GrResourceCache gets
external flush notifications in a coming CL.

[bsalomon, 2016-09-08 18:02:31]

when you get a chance, this is a pretty small one.

[robertphillips, 2016-09-08 18:05:27]

lgtm.

[bsalomon, 2016-09-08 18:07:33]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2016-09-08 18:07:45]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-08 18:29:01]

Description was changed from

==========
Move prepareForExternalIO implementation from GrContext to GrDrawingManager
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2324473002
==========

to

==========
Move prepareForExternalIO implementation from GrContext to GrDrawingManager
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2324473002

Committed:
https://skia.googlesource.com/skia/+/6a2b1941c1da272f704439e417f212932eed2004
==========

[commit-bot: I haz the power, 2016-09-08 18:29:02]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/6a2b1941c1da272f704439e417f212932eed2004