Revert of Re-enable ChannelMojo.

Revert of Re-enable ChannelMojo. (patchset #1 id:40001 of https://codereview.chromium.org/1273283002/ )

Reason for revert:
Still seeing flake on ChromeOS, and it's probably this again.

Original issue's description:
> Re-enable ChannelMojo.
>
> AGAIN! Previously reverted attempts:
>
> https://codereview.chromium.org/1262503011/
> https://codereview.chromium.org/1256473002/
>
> SyncMessageFilter is set up to properly use thread-safe
> Send channels now, so this should stick.
>
> Maybe.
>
> BUG=500019
> TBR=jam@chromium.org
>
> Committed: https://crrev.com/d34d184bd1a88043667b10cba79a5770bd2803fb
> Cr-Commit-Position: refs/heads/master@{#342484}

TBR=
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=500019
Committed: https://crrev.com/cba509edaa5efe5a97ead7687c7cbac363d640ff
Cr-Commit-Position: refs/heads/master@{#342526}

[Ken Rockot(use gerrit already), 2015-08-08 14:29:51]

Created Revert of Re-enable ChannelMojo.

[commit-bot: I haz the power, 2015-08-08 14:29:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1285463002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1285463002/1

[commit-bot: I haz the power, 2015-08-08 14:30:14]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-08 14:30:47]

Patchset 1 (id:??) landed as
https://crrev.com/cba509edaa5efe5a97ead7687c7cbac363d640ff
Cr-Commit-Position: refs/heads/master@{#342526}