gae_ts_mon: flush metrics asynchronously

gae_ts_mon: flush metrics asynchronously

Start flushing metrics at the beginning of a request in a parallel
thread. This reduces the overall latency of the request.

BUG=591122
R=dsansome@chromium.org, iannucci@chromium.org
TEST=load-tested in the cloud

Committed: https://chromium.googlesource.com/infra/infra/+/5d220c3d397eb320a1e451e6c40df629dae48428

[Sergey Berezin, 2016-03-08 00:55:16]

PTAL.

Evidence that it works: logs from a request that took 1.19 sec:

16:44:26.044 ts_mon: sending a proto took 0.595080 sec
16:44:26.142 ts_mon: populating metrics took 1.176080 sec

Actual metrics sent: http://shortn/_P6muS1Y2sW

[iannucci, 2016-03-08 01:09:30]

nice :) lgtm

[Sergey Berezin, 2016-03-08 01:26:30]

The CQ bit was checked by sergeyberezin@chromium.org

[commit-bot: I haz the power, 2016-03-08 01:26:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1772913003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1772913003/1

[commit-bot: I haz the power, 2016-03-08 01:30:35]

Description was changed from

==========
gae_ts_mon: flush metrics asynchronously

Start flushing metrics at the beginning of a request in a parallel
thread. This reduces the overall latency of the request.

BUG=591122
R=dsansome@chromium.org, iannucci@chromium.org
TEST=load-tested in the cloud
==========

to

==========
gae_ts_mon: flush metrics asynchronously

Start flushing metrics at the beginning of a request in a parallel
thread. This reduces the overall latency of the request.

BUG=591122
R=dsansome@chromium.org, iannucci@chromium.org
TEST=load-tested in the cloud

Committed:
https://chromium.googlesource.com/infra/infra/+/5d220c3d397eb320a1e451e6c40df...
==========

[commit-bot: I haz the power, 2016-03-08 01:30:35]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/infra/infra/+/5d220c3d397eb320a1e451e6c40df...

[dsansome, 2016-03-08 02:37:18]

lgtm