SkSurface copy-on-write can yield stale GPU render targets.

SkSurface copy-on-write can yield stale GPU render targets.

Prepare_rt_for_external_access() grabs the render target and then fires
access notifications.

But the notification handlers may trigger copy-on-write, causing the
returned render target to be stale (pointing at the detached snapshot).

We should grab the render target after firing notifications.

R=reed@google.com,bsalomon@google.com

Committed: https://skia.googlesource.com/skia/+/e2639089bddc4fbb129ae039cb12c01be087b397

[f(malita), 2015-08-05 22:25:27]

The CQ bit was checked by fmalita@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-05 22:25:45]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1276713002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1276713002/20001

[commit-bot: I haz the power, 2015-08-05 22:32:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-05 22:33:00]

Dry run: This issue passed the CQ dry run.

[f(malita), 2015-08-06 00:26:33]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2015-08-06 00:26:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1276713002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1276713002/20001

[commit-bot: I haz the power, 2015-08-06 00:26:50]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-08-06 06:26 UTC

[commit-bot: I haz the power, 2015-08-06 06:26:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-06 06:26:11]

No LGTM from a valid reviewer yet. Please ask for an LGTM from a
full Skia committer from
https://skia.googlesource.com/skia/+/master/CQ_COMMITTERS

[reed1, 2015-08-06 13:15:30]

code change seems fine.

brian - is this the cleanest way to test for cow?

[bsalomon, 2015-08-06 13:59:50]

On 2015/08/06 13:15:30, reed1 wrote:
> code change seems fine.
> 
> brian - is this the cleanest way to test for cow?

I can't think of a cleaner way unless we added some signal that cow occurred.

lgtm

[f(malita), 2015-08-06 14:04:24]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2015-08-06 14:04:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1276713002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1276713002/20001

[commit-bot: I haz the power, 2015-08-06 14:04:55]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/e2639089bddc4fbb129ae039cb12c01be087b397