Don't forward frames that can't be converted to I420.

Don't forward frames that can't be converted to I420.
This patch change VideoCaptureController to ignore buffers that cant be converted to I420.
This is mostly important for failures in MJPG decoding.

BUG=453761
Committed: https://crrev.com/e63cb64457a53eaaf4aa6637f0a7e1847ebea109
Cr-Commit-Position: refs/heads/master@{#314548}

[perkj_chrome, 2015-02-03 20:42:52]

perkj@chromium.org changed reviewers:
+ tommi@chromium.org

[perkj_chrome, 2015-02-03 20:42:52]

I found the MJPG problem. Can you please review?  It can happen on all
platforms.

[tommi (sloooow) - chröme, 2015-02-04 11:49:56]

The CQ bit was checked by tommi@chromium.org

[tommi (sloooow) - chröme, 2015-02-04 11:49:57]

lgtm

[commit-bot: I haz the power, 2015-02-04 11:51:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/882883004/20001

[commit-bot: I haz the power, 2015-02-04 12:40:50]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-04 12:42:27]

Patchset 2 (id:??) landed as
https://crrev.com/e63cb64457a53eaaf4aa6637f0a7e1847ebea109
Cr-Commit-Position: refs/heads/master@{#314548}