Revert of Removing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message.

Revert of Removing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message. (patchset #3 id:40001 of https://codereview.chromium.org/2478343002/ )

Reason for revert:
This is causing crashes in fast/hidpi/scrollbar-appearance-increase-device-scale-factor.html, more info in http://crbug.com/612500#c71.

Original issue's description:
> Replacing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message
> with a Mojo shared buffer. Mojo shared buffers automatically delegate
> to a privileged process using an internal sync IPC if necessary when
> instanciated, hence the simplification here.
>
> BUG=612500
>
> Committed: https://crrev.com/f42b5afcda825dbd4d9e278082c24578866d3c31
> Cr-Commit-Position: refs/heads/master@{#431130}

TBR=rockot@chromium.org,nasko@chromium.org,jcivelli@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=612500
Committed: https://crrev.com/0ae3afa991b953ada3e87fb2c44c65560d8b4196
Cr-Commit-Position: refs/heads/master@{#431219}

[vabr (Chromium), 2016-11-10 09:15:58]

The CQ bit was checked by vabr@chromium.org

[vabr (Chromium), 2016-11-10 09:15:58]

Created Revert of Removing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC
message.

[commit-bot: I haz the power, 2016-11-10 09:16:18]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-10 09:18:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-10 09:22:29]

Description was changed from

==========
Revert of Removing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message.
(patchset #3 id:40001 of https://codereview.chromium.org/2478343002/ )

Reason for revert:
This is causing crashes in
fast/hidpi/scrollbar-appearance-increase-device-scale-factor.html, more info in
http://crbug.com/612500#c71.

Original issue's description:
> Replacing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message
> with a Mojo shared buffer. Mojo shared buffers automatically delegate
> to a privileged process using an internal sync IPC if necessary when
> instanciated, hence the simplification here.
> 
> BUG=612500
> 
> Committed: https://crrev.com/f42b5afcda825dbd4d9e278082c24578866d3c31
> Cr-Commit-Position: refs/heads/master@{#431130}

TBR=rockot@chromium.org,nasko@chromium.org,jcivelli@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=612500
==========

to

==========
Revert of Removing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message.
(patchset #3 id:40001 of https://codereview.chromium.org/2478343002/ )

Reason for revert:
This is causing crashes in
fast/hidpi/scrollbar-appearance-increase-device-scale-factor.html, more info in
http://crbug.com/612500#c71.

Original issue's description:
> Replacing the ChildProcessHostMsg_SyncAllocateSharedMemory IPC message
> with a Mojo shared buffer. Mojo shared buffers automatically delegate
> to a privileged process using an internal sync IPC if necessary when
> instanciated, hence the simplification here.
>
> BUG=612500
>
> Committed: https://crrev.com/f42b5afcda825dbd4d9e278082c24578866d3c31
> Cr-Commit-Position: refs/heads/master@{#431130}

TBR=rockot@chromium.org,nasko@chromium.org,jcivelli@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=612500

Committed: https://crrev.com/0ae3afa991b953ada3e87fb2c44c65560d8b4196
Cr-Commit-Position: refs/heads/master@{#431219}
==========

[commit-bot: I haz the power, 2016-11-10 09:22:30]

Patchset 1 (id:??) landed as
https://crrev.com/0ae3afa991b953ada3e87fb2c44c65560d8b4196
Cr-Commit-Position: refs/heads/master@{#431219}