Revert of Revert of Mojo: Convert scoped_ptr<...>() to nullptr in mojo/embedder.

Revert of Revert of Mojo: Convert scoped_ptr<...>() to nullptr in mojo/embedder. (patchset #1 id:1 of https://codereview.chromium.org/593313006/)

Reason for revert:
scoped_ptr nullptr support was un-reverted.

Original issue's description:
> Revert of Mojo: Convert scoped_ptr<...>() to nullptr in mojo/embedder. (patchset #1 id:1 of https://codereview.chromium.org/606143003/)
>
> Reason for revert:
> scoped_ptr nullptr support was reverted.
>
> Original issue's description:
> > Mojo: Convert scoped_ptr<...>() to nullptr in mojo/embedder.
> >
> > R=jamesr@chromium.org
> >
> > Committed: https://crrev.com/1b198fa11edbe68701e12c27d5f4981398f5ca71
> > Cr-Commit-Position: refs/heads/master@{#297093}
>
> TBR=jamesr@chromium.org,viettrungluu@chromium.org
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/76577a68922585f5621db8c63ba2ab6d5aa03f69
> Cr-Commit-Position: refs/heads/master@{#297109}

TBR=jamesr@chromium.org,dcheng@chromium.org
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/b6a9b4d4355f50b44b8f400c7caf19ef2dca4f61
Cr-Commit-Position: refs/heads/master@{#297191}

[viettrungluu, 2014-09-29 16:48:15]

Created Revert of Revert of Mojo: Convert scoped_ptr<...>() to nullptr in
mojo/embedder.

[commit-bot: I haz the power, 2014-09-29 16:48:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/612923002/1

[commit-bot: I haz the power, 2014-09-29 16:49:10]

Committed patchset #1 (id:1) as a7bc1542a7620edbc083faac291eef134b017afb

[commit-bot: I haz the power, 2014-09-29 16:49:55]

Patchset 1 (id:??) landed as
https://crrev.com/b6a9b4d4355f50b44b8f400c7caf19ef2dca4f61
Cr-Commit-Position: refs/heads/master@{#297191}