Revert of Re-enable ChannelMojo

Revert of Re-enable ChannelMojo (patchset #1 id:20001 of https://codereview.chromium.org/1262503011/ )

Reason for revert:
Suspecting this CL causes many Layout test failures (https://crbug.com/517391).

Original issue's description:
> Re-enable ChannelMojo
>
> The performance regression seen previously was probably
> misattributed to ChannelMojo. Also, given that a great deal of
> code will now take advantage of the channel's thread-safe Send,
> this is expected to result in an net performance improvement.
>
> BUG=500019
> TBR=jam@chromium.org
>
> Committed: https://crrev.com/ab1a53c964a77dabb6d08b7199111b51a330885e
> Cr-Commit-Position: refs/heads/master@{#342055}

TBR=rockot@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=500019
Committed: https://crrev.com/a116e2287895078d72b2766ab1ac44582b27a7c6
Cr-Commit-Position: refs/heads/master@{#342085}

[hiroshige, 2015-08-06 09:27:39]

Created Revert of Re-enable ChannelMojo

[commit-bot: I haz the power, 2015-08-06 09:27:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1265383006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1265383006/1

[commit-bot: I haz the power, 2015-08-06 09:28:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-06 09:29:06]

Patchset 1 (id:??) landed as
https://crrev.com/a116e2287895078d72b2766ab1ac44582b27a7c6
Cr-Commit-Position: refs/heads/master@{#342085}