media: VideoRendererImplTest: wait on buffering change to exit first step

media: VideoRendererImplTest: wait on buffering change to exit first step

The buffering state change is the last callback fired by
VideoRendererImpl, therefore we should wait on this rather than the
paint callback.

BUG=470517
Committed: https://crrev.com/da2b3023e8da766d258331f80a003c73df06be09
Cr-Commit-Position: refs/heads/master@{#322627}

[llandwerlin-old, 2015-03-27 17:45:25]

PTAL, another try at fixing the DrMemory bots. Thanks.

[llandwerlin-old, 2015-03-27 17:45:41]

lionel.g.landwerlin@intel.com changed reviewers:
+ dalecurtis@chromium.org

[DaleCurtis, 2015-03-27 18:13:31]

lgtm

[llandwerlin-old, 2015-03-27 19:28:26]

The CQ bit was checked by lionel.g.landwerlin@intel.com

[commit-bot: I haz the power, 2015-03-27 19:29:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1042473002/1

[commit-bot: I haz the power, 2015-03-27 19:59:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-27 20:00:10]

Patchset 1 (id:??) landed as
https://crrev.com/da2b3023e8da766d258331f80a003c73df06be09
Cr-Commit-Position: refs/heads/master@{#322627}