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

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}

[dcheng, 2014-09-27 07:42:16]

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

[commit-bot: I haz the power, 2014-09-27 07:43:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/593313006/1

[commit-bot: I haz the power, 2014-09-27 07:43:34]

Committed patchset #1 (id:1) as 4b015b870dd697bb5b6e10c3f46d30c9da5788ba

[commit-bot: I haz the power, 2014-09-27 07:44:34]

Patchset 1 (id:??) landed as
https://crrev.com/76577a68922585f5621db8c63ba2ab6d5aa03f69
Cr-Commit-Position: refs/heads/master@{#297109}

[viettrungluu, 2014-09-29 16:48:14]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/612923002/ by viettrungluu@chromium.org.

The reason for reverting is: scoped_ptr nullptr support was un-reverted..