Revert of ipc: Clean up interface of attachment broker.

Revert of ipc: Clean up interface of attachment broker. (patchset #5 id:80001 of https://codereview.chromium.org/1269553003/)

Reason for revert:
Causes errors on win7.

http://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/40371

Original issue's description:
> ipc: Clean up interface of attachment broker.
> 
> AttachmentBrokerUnprivileged now has a method
> DesignateBrokerCommunicationChannel which is used by non-broker processes to
> designate an IPC::Channel as the communication medium for brokerable attachment
> messages. IPC::Channel has a new member attachment_broker_endpoint_ which causes
> it to pass all messages through the attachment broker before forwarding them to
> the listener.
> 
> BUG=493414
> 
> Committed: https://crrev.com/9a06836982214f2edced21bbd1615b49e7f231bf
> Cr-Commit-Position: refs/heads/master@{#341143}

TBR=tsepez@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=493414

[erikchen, 2015-07-30 20:48:44]

Created Revert of ipc: Clean up interface of attachment broker.

[commit-bot: I haz the power, 2015-07-30 20:49:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1264543003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1264543003/1

[erikchen, 2015-07-30 20:50:21]

The CQ bit was unchecked by erikchen@chromium.org

[commit-bot: I haz the power, 2015-07-30 20:50:53]

Failed to apply the patch.

[erikchen, 2015-07-30 20:52:01]

On 2015/07/30 20:50:53, commit-bot: I haz the power wrote:
> Failed to apply the patch.

Already reverted.