Add metrics for tracking underflow during src= playback.

Add metrics for tracking underflow during src= playback.

I'm surprised we didn't already have these metrics, they are pretty
key to evaluating improvements to our pipeline. Possibly they were
harder to add prior to chcunningham@'s recent work to expose the
BUFFERING_HAVE_NOTHING state to WMPI.

BUG=641633
TEST=manual.

Committed: https://crrev.com/9d638a1ee2933e62dccaed16eef64e64cbe2ded9
Cr-Commit-Position: refs/heads/master@{#415215}

[DaleCurtis, 2016-08-27 00:27:43]

dalecurtis@chromium.org changed reviewers:
+ chcunningham@chromium.org, holte@chromium.org

[chcunningham, 2016-08-29 17:24:25]

Just a reminder, in addition to network underflow this will also be triggered
whenever our decoders fall behind. I'd still like to take separating these in
the near future.

LGTM

[DaleCurtis, 2016-08-29 21:19:24]

holte@ ping?

[Steven Holte, 2016-08-29 22:34:35]

lgtm

[DaleCurtis, 2016-08-29 22:39:55]

The CQ bit was checked by dalecurtis@chromium.org

[commit-bot: I haz the power, 2016-08-29 23:30:57]

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

[commit-bot: I haz the power, 2016-08-30 06:21:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-30 06:24:29]

Description was changed from

==========
Add metrics for tracking underflow during src= playback.

I'm surprised we didn't already have these metrics, they are pretty
key to evaluating improvements to our pipeline. Possibly they were
harder to add prior to chcunningham@'s recent work to expose the
BUFFERING_HAVE_NOTHING state to WMPI.

BUG=641633
TEST=manual.
==========

to

==========
Add metrics for tracking underflow during src= playback.

I'm surprised we didn't already have these metrics, they are pretty
key to evaluating improvements to our pipeline. Possibly they were
harder to add prior to chcunningham@'s recent work to expose the
BUFFERING_HAVE_NOTHING state to WMPI.

BUG=641633
TEST=manual.

Committed: https://crrev.com/9d638a1ee2933e62dccaed16eef64e64cbe2ded9
Cr-Commit-Position: refs/heads/master@{#415215}
==========

[commit-bot: I haz the power, 2016-08-30 06:24:31]

Patchset 1 (id:??) landed as
https://crrev.com/9d638a1ee2933e62dccaed16eef64e64cbe2ded9
Cr-Commit-Position: refs/heads/master@{#415215}