Cast: Clarify the unit of bitrate

Cast: Clarify the unit of bitrate

This change is to clarify the unit used in cast.streaming APIs for
bitrate. It should be in kilobits per second. And the unit conversion
should be done just before converting to VideoSenderConfig and
AudioSenderConfig which use bits per second as unit.

This will improve the video quality for existing extensions which use
kilobits per second.

BUG=354267
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=260438

[not at google - send to devlin, 2014-03-27 19:39:43]

lgtm

[Alpha Left Google, 2014-03-27 20:37:45]

The CQ bit was checked by hclam@chromium.org

[commit-bot: I haz the power, 2014-03-27 20:41:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hclam@chromium.org/214663008/1

[hshi1, 2014-03-28 21:15:26]

The CQ bit was unchecked by hshi@chromium.org

[hshi1, 2014-03-28 21:15:36]

The CQ bit was checked by hshi@chromium.org

[cmp, 2014-03-30 17:00:09]

The CQ bit was unchecked by cmp@chromium.org

[cmp, 2014-03-30 17:02:20]

The CQ bit was checked by cmp@chromium.org

[cmp, 2014-03-30 17:03:41]

The CQ bit was unchecked by cmp@chromium.org

[cmp, 2014-03-30 17:07:23]

The CQ bit was checked by cmp@chromium.org

[commit-bot: I haz the power, 2014-03-30 17:07:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hclam@chromium.org/214663008/1

[commit-bot: I haz the power, 2014-03-30 17:10:01]

Change committed as 260438