[cast] Force 4:2:0 pixel formats in H264VideoToolboxEncoder.

[cast] Force 4:2:0 pixel formats in H264VideoToolboxEncoder.

On some platforms, notably the iOS simulator, VideoToolbox compression
sessions vend 4:2:2 pixel buffers by default. This is not supported by
the VideoFrame-CVPixelBuffer integration code.

This patch forces VideoToolbox to vend I420 or NV12 buffers. For
encoders that natively support those formats, this effectively changes
nothing. For encoders that do not, VideoToolbox will convert submitted
frames to whatever format the encoder wants.

In practice, this is a defensive patch that also allows testing iOS cast
streaming on the iOS simulator.

BUG=450804
R=miu, hclam

Committed: https://crrev.com/8813c543acf046b68183d32ef5321bce882db586
Cr-Commit-Position: refs/heads/master@{#313103}

[miu, 2015-01-22 00:01:22]

lgtm

https://codereview.chromium.org/859303004/diff/1/media/cast/sender/h264_vt_en...
File media/cast/sender/h264_vt_encoder.cc (right):

https://codereview.chromium.org/859303004/diff/1/media/cast/sender/h264_vt_en...
media/cast/sender/h264_vt_encoder.cc:278: const int formats[] = {
Wow.  This is all a bit heavy-weight to pass in an Array of integers.  But, I
blame Apple, not you.  ;-)

[jfroy, 2015-01-22 17:17:20]

The CQ bit was checked by jfroy@chromium.org

[commit-bot: I haz the power, 2015-01-22 17:18:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/859303004/20001

[commit-bot: I haz the power, 2015-01-22 19:41:42]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-22 19:41:43]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[jfroy, 2015-01-22 19:44:24]

Unrelated test (PolicyPathParserTests.AllPlatformVariables) is failing on
mac_chromium_rel_ng. I'll rebase and wait a little bit.

[jfroy, 2015-01-23 22:53:25]

The CQ bit was checked by jfroy@chromium.org

[commit-bot: I haz the power, 2015-01-23 22:54:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/859303004/20001

[commit-bot: I haz the power, 2015-01-23 22:55:00]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-23 22:55:00]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[jfroy, 2015-01-26 19:01:45]

The CQ bit was checked by jfroy@chromium.org

[commit-bot: I haz the power, 2015-01-26 19:02:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/859303004/40001

[commit-bot: I haz the power, 2015-01-26 19:51:25]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-01-26 19:52:21]

Patchset 3 (id:??) landed as
https://crrev.com/8813c543acf046b68183d32ef5321bce882db586
Cr-Commit-Position: refs/heads/master@{#313103}