Ensure that SequencedWorkerPools in tests don't outlive their tests

Ensure that SequencedWorkerPools in tests don't outlive their tests

This prevents strange races with other tests.

Add an OnDestroy() method to SequencedWorkerPool::TestingObserver().

Fix a bug where one test wasn't calling Shutdown() on its
WorkerPools.

Fix a deadlock if a Worker object releases the last ref to the WorkerPool.

BUG=115987
TEST=


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=125152

[akalin, 2012-03-01 00:14:21]

+brettw for review

[akalin, 2012-03-01 11:34:20]

On 2012/03/01 00:14:21, akalin wrote:
> +brettw for review

Hold off on the review, looks like I have some bugs to fix first.

[akalin, 2012-03-01 21:28:06]

On 2012/03/01 11:34:20, akalin wrote:
> On 2012/03/01 00:14:21, akalin wrote:
> > +brettw for review
> 
> Hold off on the review, looks like I have some bugs to fix first.

Okay, should be good to review now.  PTAL!

[brettw, 2012-03-02 05:39:03]

lgtm

[commit-bot: I haz the power, 2012-03-06 07:21:30]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/akalin@chromium.org/9558007/22003

[commit-bot: I haz the power, 2012-03-06 08:14:27]

Try job failure for 9558007-22003 (retry) on linux_rel for step
"content_unittests".
It's a second try, previously, step "content_unittests" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2012-03-06 10:03:07]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/akalin@chromium.org/9558007/31001

[commit-bot: I haz the power, 2012-03-06 14:17:36]

Change committed as 125152