Allow nested state restorers in DrawingBuffer

Allow nested state restorers in DrawingBuffer

State restoration required in callbacks that can come from
DrawingBuffer. This allows us to construct a stack of restorers.

BUG=658265
Committed: https://crrev.com/7946e681411fb3144eac23476d75a837d6db39b4
Cr-Commit-Position: refs/heads/master@{#428283}

[ccameron, 2016-10-27 06:36:00]

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

[commit-bot: I haz the power, 2016-10-27 06:36:18]

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

[ccameron, 2016-10-27 06:38:23]

ccameron@chromium.org changed reviewers:
+ kbr@chromium.org

[ccameron, 2016-10-27 06:38:23]

This is the promised cleanup from earlier.

We can indeed call back into DrawingBuffer's public interface from within
DrawingBuffer, so we should allow for nested state restorers.

[commit-bot: I haz the power, 2016-10-27 09:22:37]

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

[commit-bot: I haz the power, 2016-10-27 09:22:38]

Dry run: This issue passed the CQ dry run.

[Ken Russell (switch to Gerrit), 2016-10-28 00:23:50]

Excellent. Thanks for following up on this. LGTM

[ccameron, 2016-10-28 04:29:16]

The CQ bit was checked by ccameron@chromium.org

[commit-bot: I haz the power, 2016-10-28 04:29:36]

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, 2016-10-28 04:34:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-28 04:37:06]

Description was changed from

==========
Allow nested state restorers in DrawingBuffer

State restoration required in callbacks that can come from
DrawingBuffer. This allows us to construct a stack of restorers.

BUG=658265
==========

to

==========
Allow nested state restorers in DrawingBuffer

State restoration required in callbacks that can come from
DrawingBuffer. This allows us to construct a stack of restorers.

BUG=658265

Committed: https://crrev.com/7946e681411fb3144eac23476d75a837d6db39b4
Cr-Commit-Position: refs/heads/master@{#428283}
==========

[commit-bot: I haz the power, 2016-10-28 04:37:07]

Patchset 1 (id:??) landed as
https://crrev.com/7946e681411fb3144eac23476d75a837d6db39b4
Cr-Commit-Position: refs/heads/master@{#428283}