Change MediaStreamTrack::getSources to go through UserMediaClient.

Change MediaStreamTrack::getSources to go through UserMediaClient.

This makes MediaStreamTrack::getSources go through UserMediaClient instead, needed to know which frame the call came from.

Depending on:
Blink CL part 1: https://codereview.chromium.org/560843002
Chrome CL part 1: https://codereview.chromium.org/562643003/
Chrome CL part 2: https://codereview.chromium.org/564423002/

BUG=406094
NOTRY=true

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=182141

[Henrik Grunell, 2014-09-11 13:06:33]

grunell@chromium.org changed reviewers:
+ jochen@chromium.org

[Henrik Grunell, 2014-09-11 13:09:51]

This is just a break-out of https://codereview.chromium.org/560843002/ which you
already reviewed and lgtm'd.

[jochen (gone - plz use gerrit), 2014-09-11 13:19:14]

lgtm

[Henrik Grunell, 2014-09-15 08:45:37]

The CQ bit was checked by grunell@chromium.org

[commit-bot: I haz the power, 2014-09-15 08:45:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/559423002/20001

[commit-bot: I haz the power, 2014-09-15 08:56:08]

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

[commit-bot: I haz the power, 2014-09-15 08:56:09]

Try jobs failed on following builders:
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/55890)

[Henrik Grunell, 2014-09-16 17:16:19]

The CQ bit was checked by grunell@chromium.org

[commit-bot: I haz the power, 2014-09-16 17:16:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/559423002/40001

[commit-bot: I haz the power, 2014-09-16 19:17:42]

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

[commit-bot: I haz the power, 2014-09-16 19:17:43]

Exceeded time limit waiting for builds to trigger.

[Henrik Grunell, 2014-09-17 08:34:03]

The CQ bit was checked by grunell@chromium.org

[commit-bot: I haz the power, 2014-09-17 08:35:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/559423002/40001

[Henrik Grunell, 2014-09-17 08:35:02]

The CQ bit was unchecked by grunell@chromium.org

[commit-bot: I haz the power, 2014-09-17 08:35:14]

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

[Henrik Grunell, 2014-09-17 08:35:32]

The CQ bit was checked by grunell@chromium.org

[commit-bot: I haz the power, 2014-09-17 08:35:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/559423002/60001

[commit-bot: I haz the power, 2014-09-17 08:36:04]

Committed patchset #4 (id:60001) as 182141