Revert of Moving MediaStreamSignaling logic into PeerConnection.

Revert of Moving MediaStreamSignaling logic into PeerConnection. (patchset #10 id:180001 of https://codereview.webrtc.org/1393563002/ )

Reason for revert:
Broke browser_tests on Mac. Still need to investigate the cause.

Original issue's description:
> Moving MediaStreamSignaling logic into PeerConnection.
>
> This needs to happen because in the future, m-lines will be offered
> based on the set of RtpSenders/RtpReceivers, rather than the set of
> tracks that MediaStreamSignaling knows about.
>
> Besides that, MediaStreamSignaling was a "glue class" without
> a clearly defined role, so it going away is good for other
> reasons as well.
>
> Committed: https://crrev.com/97c392935411398b506861601c82e31d95c591f0
> Cr-Commit-Position: refs/heads/master@{#10268}

TBR=pthatcher@webrtc.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/fc648b6d934e936f4d9a32c813364b331536ec3b
Cr-Commit-Position: refs/heads/master@{#10269}

[Taylor Brandstetter, 2015-10-13 23:41:50]

Created Revert of Moving MediaStreamSignaling logic into PeerConnection.

[commit-bot: I haz the power, 2015-10-13 23:42:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1403633005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1403633005/1

[commit-bot: I haz the power, 2015-10-13 23:43:10]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-13 23:43:30]

Patchset 1 (id:??) landed as
https://crrev.com/fc648b6d934e936f4d9a32c813364b331536ec3b
Cr-Commit-Position: refs/heads/master@{#10269}

[Taylor Brandstetter, 2015-10-14 00:24:07]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.webrtc.org/1404473005/ by deadbeef@webrtc.org.

The reason for reverting is: ..