NetEq: Implement two UMA stats for delay adaptation.

NetEq: Implement two UMA stats for delay adaptation.

This CL adds calculation and logging of average excess buffer delay
and number of delayed packet outage events per minute.

The first is the average of time spent in the packet buffer for all
packets. The average is calculated for intervals of one minute, and
the result is logged to the UMA stat
WebRTC.Audio.AverageExcessBufferDelayMs.

The second is a counter of delayed packet outage events that is
restarted every minute, and the result is logged to the UMA stat
WebRTC.Audio.DelayedPacketOutageEventsPerMinute. For a description of
delayed packet outages, see previous CL implementing a duration log
for these events.

BUG=webrtc:4915, chromium:488124
R=minyue@webrtc.org

Committed: https://chromium.googlesource.com/external/webrtc/+/1f4ffe02fb565cc29e4d5c1d1a3423e9eff9c4ab

[hlundin-webrtc, 2015-08-18 13:30:41]

henrik.lundin@webrtc.org changed reviewers:
+ ivoc@webrtc.org, minyue@webrtc.org

[hlundin-webrtc, 2015-08-18 13:30:41]

henrik.lundin@webrtc.org changed required reviewers:
+ minyue@webrtc.org

[hlundin-webrtc, 2015-08-18 13:30:41]

Please, review this change. It replaces
https://codereview.webrtc.org/1292423003/ and
https://codereview.webrtc.org/1284303003/ which will both be dropped.

Thanks!
/HL

[minyue-webrtc, 2015-08-18 14:06:10]

lgtm

clean and neat!

[hlundin-webrtc, 2015-08-19 07:46:26]

The CQ bit was checked by henrik.lundin@webrtc.org

[commit-bot: I haz the power, 2015-08-19 07:46:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1287333005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1287333005/1

[commit-bot: I haz the power, 2015-08-19 08:02:03]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-19 08:02:03]

Try jobs failed on following builders:
  linux_rel on tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/linux_rel/builds/8908)

[hlundin-webrtc, 2015-08-19 08:47:07]

Committed patchset #1 (id:1) manually as
1f4ffe02fb565cc29e4d5c1d1a3423e9eff9c4ab (presubmit successful).