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 failures in:

IPCAttachmentBrokerPrivilegedWinTest.SendHandle
IPCAttachmentBrokerPrivilegedWinTest.SendHandleToSelf
IPCAttachmentBrokerPrivilegedWinTest.SendHandleWithoutPermissions

on the Win7 Tests (dbg)(1) bot

http://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/40372/steps/ipc_tests/logs/stdio

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,erikchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=493414
Committed: https://crrev.com/090599613215def05230b90969a5747f0f06315a
Cr-Commit-Position: refs/heads/master@{#341171}

[Avi (use Gerrit), 2015-07-30 19:37:45]

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

[commit-bot: I haz the power, 2015-07-30 19:39:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1259953005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1259953005/1

[commit-bot: I haz the power, 2015-07-30 19:40:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-30 19:41:26]

Patchset 1 (id:??) landed as
https://crrev.com/090599613215def05230b90969a5747f0f06315a
Cr-Commit-Position: refs/heads/master@{#341171}