Revert of Reland #1 "ipc: Add a new field num_brokered_attachments to the message header."

Revert of Reland #1 "ipc: Add a new field num_brokered_attachments to the message header." (patchset #4 id:60001 of https://codereview.chromium.org/1330563002/ )

Reason for revert:
This CL was only ever intended to make it into one Canary.

Original issue's description:
> Reland #1 "ipc: Add a new field num_brokered_attachments to the message header."
>
> This otherwise innocuous CL is causing an unusual crash in Canary. At first
> glance, the crash appears related to IPC, but further digging indicates that
> it's probably related to corruption of a ResourceBuffer. I've updated that class
> to use CHECKs instead of DCHECKs https://codereview.chromium.org/1325153002/.
>
> I expect this CL to cause ~100 crashes in the next Chrome Canary. I intend to
> revert this CL after a single Canary release. This CL will help me better
> diagnose the exact nature of the crash.
>
> BUG=493414
>
> Committed: https://crrev.com/d32c32bef61d80f68208e550ace18f50f1c498d1
> Cr-Commit-Position: refs/heads/master@{#347250}

TBR=tsepez@chromium.org,avi@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=493414
Committed: https://crrev.com/3086a2e4a27aa39f38b7c5aab6bf8c2815092adf
Cr-Commit-Position: refs/heads/master@{#347429}

[erikchen, 2015-09-04 16:56:40]

Created Revert of Reland #1 "ipc: Add a new field num_brokered_attachments to
the message header."

[commit-bot: I haz the power, 2015-09-04 16:56:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1314803005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1314803005/1

[commit-bot: I haz the power, 2015-09-04 16:57:42]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-04 16:58:31]

Patchset 1 (id:??) landed as
https://crrev.com/3086a2e4a27aa39f38b7c5aab6bf8c2815092adf
Cr-Commit-Position: refs/heads/master@{#347429}