Replace the only use of media::MockStatisticsCB with a bound method.

Replace the only use of media::MockStatisticsCB with a bound method.

No need to keep useless helper mocks around. This also helps clean up
VideoRendererImpl's unit tests in preparation for switching to the
scheduler.

Committed: https://crrev.com/c13ad6e22d9f25956827e5d61f0fd55a9e403359
Cr-Commit-Position: refs/heads/master@{#294704}

[scherkus (not reviewing), 2014-09-12 21:19:48]

scherkus@chromium.org changed reviewers:
+ dalecurtis@chromium.org

[DaleCurtis, 2014-09-12 21:25:03]

lgtm

[scherkus (not reviewing), 2014-09-12 21:25:33]

The CQ bit was checked by scherkus@chromium.org

[commit-bot: I haz the power, 2014-09-12 21:31:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/566853006/1

[commit-bot: I haz the power, 2014-09-13 00:42:31]

Committed patchset #1 (id:1) as 2552a41e77c24148ca84be33754b504a38593529

[commit-bot: I haz the power, 2014-09-13 00:47:44]

Patchset 1 (id:??) landed as
https://crrev.com/c13ad6e22d9f25956827e5d61f0fd55a9e403359
Cr-Commit-Position: refs/heads/master@{#294704}