Fix race in EmbeddedApplicationRunner::ShutDown

Fix race in EmbeddedApplicationRunner::ShutDown

Joins the application thread before resetting the stored TaskRunner
reference. Avoids a nullptr dereference if ShutDown is called
immediately after BindServiceRequest but before the posted task
has run.

BUG=626299
TBR=ben@chromium.org

Committed: https://crrev.com/5265f8ef11e3205bdbbd0178f8c739e6e39973b7
Cr-Commit-Position: refs/heads/master@{#404713}

[Ken Rockot(use gerrit already), 2016-07-11 17:55:39]

Description was changed from

==========
Fix race in EmbeddedApplicationRunner::ShutDown

Joins the application thread before resetting the stored TaskRunner
reference. Avoids a nullptr dereference if ShutDown is called
immediately after BindServiceRequest but before the posted task
has run.

BUG=626299
==========

to

==========
Fix race in EmbeddedApplicationRunner::ShutDown

Joins the application thread before resetting the stored TaskRunner
reference. Avoids a nullptr dereference if ShutDown is called
immediately after BindServiceRequest but before the posted task
has run.

BUG=626299
TBR=ben@chromium.org
==========

[Ken Rockot(use gerrit already), 2016-07-11 17:56:29]

The CQ bit was checked by rockot@chromium.org

[commit-bot: I haz the power, 2016-07-11 17:56:51]

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

[Ken Rockot(use gerrit already), 2016-07-11 17:57:50]

TBRing since: change is trivial, ben is the right reviewer, fixes a crash, and
ben is OOO.

[commit-bot: I haz the power, 2016-07-11 19:57:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-07-11 20:02:51]

Description was changed from

==========
Fix race in EmbeddedApplicationRunner::ShutDown

Joins the application thread before resetting the stored TaskRunner
reference. Avoids a nullptr dereference if ShutDown is called
immediately after BindServiceRequest but before the posted task
has run.

BUG=626299
TBR=ben@chromium.org
==========

to

==========
Fix race in EmbeddedApplicationRunner::ShutDown

Joins the application thread before resetting the stored TaskRunner
reference. Avoids a nullptr dereference if ShutDown is called
immediately after BindServiceRequest but before the posted task
has run.

BUG=626299
TBR=ben@chromium.org

Committed: https://crrev.com/5265f8ef11e3205bdbbd0178f8c739e6e39973b7
Cr-Commit-Position: refs/heads/master@{#404713}
==========

[commit-bot: I haz the power, 2016-07-11 20:02:52]

Patchset 1 (id:??) landed as
https://crrev.com/5265f8ef11e3205bdbbd0178f8c739e6e39973b7
Cr-Commit-Position: refs/heads/master@{#404713}