Avoid race in Call destructor

Avoid race in Call destructor

Don't update histograms until we're sure process threads won't call into
the instance being destructed, trying to update stats.

BUG=webrtc:6103
Committed: https://crrev.com/6d6122b46122ca45873383581a0eca8f616165ca
Cr-Commit-Position: refs/heads/master@{#13461}

[sprang_webrtc, 2016-07-13 12:32:03]

sprang@webrtc.org changed reviewers:
+ pbos@webrtc.org

[pbos-webrtc, 2016-07-13 12:38:30]

lgtm, but add a comment so this stays in place in the future

[sprang_webrtc, 2016-07-13 12:43:22]

The CQ bit was checked by sprang@webrtc.org

[sprang_webrtc, 2016-07-13 12:43:22]

The patchset sent to the CQ was uploaded after l-g-t-m from pbos@webrtc.org
Link to the patchset: https://codereview.webrtc.org/2151433002/#ps20001 (title:
"Added comment")

[commit-bot: I haz the power, 2016-07-13 12:43:26]

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

[commit-bot: I haz the power, 2016-07-13 13:37:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-07-13 13:37:19]

Description was changed from

==========
Avoid race in Call destructor

Don't update histograms until we're sure process threads won't call into
the instance being destructed, trying to update stats.

BUG=webrtc:6103
==========

to

==========
Avoid race in Call destructor

Don't update histograms until we're sure process threads won't call into
the instance being destructed, trying to update stats.

BUG=webrtc:6103

Committed: https://crrev.com/6d6122b46122ca45873383581a0eca8f616165ca
Cr-Commit-Position: refs/heads/master@{#13461}
==========

[commit-bot: I haz the power, 2016-07-13 13:37:20]

Patchset 2 (id:??) landed as
https://crrev.com/6d6122b46122ca45873383581a0eca8f616165ca
Cr-Commit-Position: refs/heads/master@{#13461}