Revert of Revert of content: Fix single process support for native GpuMemoryBuffers.

Revert of Revert of content: Fix single process support for native GpuMemoryBuffers. (patchset #1 id:1 of https://codereview.chromium.org/1210073003/)

Reason for revert:
Reverting the revert since this wasn't the problem after all.

Original issue's description:
> Revert of content: Fix single process support for native GpuMemoryBuffers. (patchset #1 id:1 of https://codereview.chromium.org/1221473003/)
>
> Reason for revert:
> XP_tests started failing with "missing shard" exceptions. Suspect this cl.
>
> https://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/38438
>
> Original issue's description:
> > content: Fix single process support for native GpuMemoryBuffers.
> >
> > Also add the startup message filter for CreateGpuMemoryBuffer
> > messages in single process mode.
> >
> > BUG=497559, 504121
> >
> > Committed: https://crrev.com/29ec87df6cef29b9f28dd21d385f16ce99df9ce3
> > Cr-Commit-Position: refs/heads/master@{#336495}
>
> TBR=piman@chromium.org,reveman@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=497559, 504121
>
> Committed: https://crrev.com/1cf221f6cebc8850220100c24d00a18ad54bfe8d
> Cr-Commit-Position: refs/heads/master@{#336531}

TBR=piman@chromium.org,reveman@chromium.org,kcarattini@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=497559, 504121
Committed: https://crrev.com/8c64842afac7b46fd5842de1e3b6b4af24d98bc2
Cr-Commit-Position: refs/heads/master@{#336593}

[grt (UTC plus 2), 2015-06-29 18:13:04]

Created Revert of Revert of content: Fix single process support for native
GpuMemoryBuffers.

[commit-bot: I haz the power, 2015-06-29 18:15:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1218783003/1

[commit-bot: I haz the power, 2015-06-29 18:17:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-29 18:19:04]

Patchset 1 (id:??) landed as
https://crrev.com/8c64842afac7b46fd5842de1e3b6b4af24d98bc2
Cr-Commit-Position: refs/heads/master@{#336593}