Adds some code to help isolate where crash is happening

Adds some code to help isolate where crash is happening

I would prefer to use tracked_objects::Location for this, but we don't
want mojo public apis to depend upon base. I may have to plumb
something similar through if this doesn't pan out.

BUG=534719
TEST=none

Committed: https://crrev.com/20033018f07a6708eec6611955428dc47c4c1220
Cr-Commit-Position: refs/heads/master@{#350917}

[sky, 2015-09-25 16:09:37]

sky@chromium.org changed reviewers:
+ jam@chromium.org

[jam, 2015-09-25 19:41:14]

lgtm

[sky, 2015-09-25 19:44:11]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2015-09-25 19:44:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1358163006/80001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1358163006/80001

[commit-bot: I haz the power, 2015-09-25 21:25:59]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2015-09-25 21:26:52]

Patchset 5 (id:??) landed as
https://crrev.com/20033018f07a6708eec6611955428dc47c4c1220
Cr-Commit-Position: refs/heads/master@{#350917}