Ensure OAuth2TokenServiceRequest::Core is destroyed on owner thread.

Ensure OAuth2TokenServiceRequest::Core is destroyed on owner thread.

This change fixes a long standing race condition where Core could be
destroyed on either the owner thread or the task runner thread.

See related discussion in https://codereview.chromium.org/12647008/

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=275263

[maniscalco, 2014-06-04 18:29:53]

This patch is meant to address the bug blundell pointed out in
https://codereview.chromium.org/299943003/.

blundell, I believe this is the fix you were describing, correct me if I'm
wrong.

Please review!

[Roger Tawa OOO till Jul 10th, 2014-06-04 18:54:18]

lgtm

[blundell, 2014-06-05 09:08:57]

lgtm

The more that I look at this code, the odder I find it :). Why does the
NonThreadSafe class have methods called on multiple threads :)? (I know you
didn't introduce this behavior).

[maniscalco, 2014-06-05 15:58:09]

On 2014/06/05 09:08:57, blundell wrote:
> lgtm
> 
> The more that I look at this code, the odder I find it :). Why does the
> NonThreadSafe class have methods called on multiple threads :)? (I know you
> didn't introduce this behavior).

A ThreadChecker data member is probably a better fit since it allows us to get
the same checks without giving a false impression that Core should never be
accessed from multiple threads.

[maniscalco, 2014-06-05 15:58:18]

The CQ bit was checked by maniscalco@chromium.org

[commit-bot: I haz the power, 2014-06-05 15:59:12]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/maniscalco@chromium.org/317773003/20001

[commit-bot: I haz the power, 2014-06-05 22:38:17]

Change committed as 275263