Revert of Refactor RtcDataChannelHandler.

Revert of Refactor RtcDataChannelHandler. (patchset #2 id:20001 of https://codereview.chromium.org/643693007/)

Reason for revert:
Broke some webrtc tests on win7

Original issue's description:
> Refactor RtcDataChannelHandler.
> This change splits the WebRtc observer functionality of RtcDataChannelHandler
> from the WebKit related functionality. The former belongs with libjingle's
> signaling thread and the latter with the main thread. As is, these threads
> are one and the same, but this will change later this week.
>
> BUG=369796
>
> Committed: https://crrev.com/832aa011fa8f98972f04468216dd2fbbd3e7ca42
> Cr-Commit-Position: refs/heads/master@{#301831}

TBR=perkj@chromium.org,tommi@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=369796
Committed: https://crrev.com/e5c86de0b8af3f3e913408c8ad7dca57a894ba6d
Cr-Commit-Position: refs/heads/master@{#301846}

[csharp, 2014-10-29 15:59:21]

Created Revert of Refactor RtcDataChannelHandler.

[commit-bot: I haz the power, 2014-10-29 16:00:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/686183002/1

[commit-bot: I haz the power, 2014-10-29 16:01:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-29 16:02:14]

Patchset 1 (id:??) landed as
https://crrev.com/e5c86de0b8af3f3e913408c8ad7dca57a894ba6d
Cr-Commit-Position: refs/heads/master@{#301846}