Revert of ipc: Change the timing of the construction of the attachment broker.

Revert of ipc: Change the timing of the construction of the attachment broker. (patchset #3 id:40001 of https://codereview.chromium.org/1367013003/ )

Reason for revert:
Still causes problems in at least one Dr. Memory test. https://code.google.com/p/chromium/issues/detail?id=536891
Requires further investigation - Reverting for now

Original issue's description:
> ipc: Change the timing of the construction of the attachment broker.
>
> This CL ensures that the privileged attachment broker is constructed earlier in
> the process of creating a child process. This fixes a race condition for single
> process mode where the child thread's attachment broker would become the global
> attachment broker.
>
> BUG=534539
>
> Committed: https://crrev.com/8758b4bd5bd210552606fa39d084aef7e786abd1
> Cr-Commit-Position: refs/heads/master@{#350899}

TBR=avi@chromium.org,tsepez@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=534539
Committed: https://crrev.com/33f19091a0fcd48e91c88abf39f2a8293e8b0fd1
Cr-Commit-Position: refs/heads/master@{#351128}

[erikchen, 2015-09-28 20:25:06]

Created Revert of ipc: Change the timing of the construction of the attachment
broker.

[commit-bot: I haz the power, 2015-09-28 20:25:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1373993002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1373993002/1

[commit-bot: I haz the power, 2015-09-28 20:27:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-28 20:28:27]

Patchset 1 (id:??) landed as
https://crrev.com/33f19091a0fcd48e91c88abf39f2a8293e8b0fd1
Cr-Commit-Position: refs/heads/master@{#351128}