Add error struct to support the setSinkId operation for WebMediaPlayer.

Add error struct to support the setSinkId operation for WebMediaPlayer.

A value of this struct will be returned to WebMediaPlayer in a callback.

This is intended to support the Audio Output Devices API
(http://w3c.github.io/mediacapture-output/)
https://www.chromestatus.com/feature/4621603249848320

BUG=438023
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197107

[Guido Urdaneta, 2015-06-13 17:58:20]

guidou@chromium.org changed reviewers:
+ mkwst@chromium.org, peter@chromium.org, tommi@chromium.org

[Guido Urdaneta, 2015-06-13 17:58:47]

Hi, please review.

[tommi (sloooow) - chröme, 2015-06-14 07:58:02]

The CQ bit was checked by tommi@chromium.org to run a CQ dry run

[tommi (sloooow) - chröme, 2015-06-14 07:58:05]

lgtm

[commit-bot: I haz the power, 2015-06-14 07:58:09]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1183803005/40001

[commit-bot: I haz the power, 2015-06-14 09:06:40]

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

[commit-bot: I haz the power, 2015-06-14 09:06:42]

Dry run: This issue passed the CQ dry run.

[Mike West, 2015-06-15 08:10:14]

public/ LGTM.

[Guido Urdaneta, 2015-06-15 08:38:03]

The CQ bit was checked by guidou@chromium.org

[commit-bot: I haz the power, 2015-06-15 08:38:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1183803005/40001

[commit-bot: I haz the power, 2015-06-15 10:01:07]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197107