Add support for redundant streams to VTVideoDecodeAccelerator.

Add support for redundant streams to VTVideoDecodeAccelerator.

In practice this means only using the first image slice to compute
|pic_order_cnt|.

BUG=133828
Committed: https://crrev.com/ba494b53d679b6d10f23eec4b945475267a72212
Cr-Commit-Position: refs/heads/master@{#306750}

[sandersd (OOO until July 31), 2014-12-04 01:30:56]

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

[DaleCurtis, 2014-12-04 01:58:15]

lgtm

[sandersd (OOO until July 31), 2014-12-04 02:06:26]

The CQ bit was checked by sandersd@chromium.org

[commit-bot: I haz the power, 2014-12-04 02:07:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/776143004/1

[commit-bot: I haz the power, 2014-12-04 02:44:00]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-04 02:44:50]

Patchset 1 (id:??) landed as
https://crrev.com/ba494b53d679b6d10f23eec4b945475267a72212
Cr-Commit-Position: refs/heads/master@{#306750}