Use auto, not const auto*, for libyuv function pointers

Use auto, not const auto*, for libyuv function pointers

This was a compiler error on GCC 4.9.1:
unable to deduce ‘const auto*’ from ‘((((content::PpFrameWriter::FrameWriterDelegate*)this)->content::PpFrameWriter::FrameWriterDelegate::endian_ == (content::PpFrameWriter::FrameWriterDelegate::PixelEndian)1u) ? libyuv::BGRAToI420 :  libyuv::ARGBToI420)’

Introduced in https://codereview.chromium.org/663183002

BUG=426020
Committed: https://crrev.com/1694f0d39e4846fbe53ea7f33943502bdd015932
Cr-Commit-Position: refs/heads/master@{#301083}

[philipj_slow, 2014-10-24 10:51:53]

philipj@opera.com changed reviewers:
+ magjed@chromium.org, perkj@chromium.org

[philipj_slow, 2014-10-24 10:51:54]

philipj@opera.com changed required reviewers:
+ perkj@chromium.org

[philipj_slow, 2014-10-24 10:51:54]

PTAL

[magjed_chromium, 2014-10-24 11:00:27]

If this works, lgtm

[philipj_slow, 2014-10-24 11:05:15]

On 2014/10/24 11:00:27, magjed wrote:
> If this works, lgtm

It works locally, let's see if the bots are happy :)

[perkj_chrome, 2014-10-24 11:17:38]

On 2014/10/24 11:05:15, philipj wrote:
> On 2014/10/24 11:00:27, magjed wrote:
> > If this works, lgtm
> 
> It works locally, let's see if the bots are happy :)

(owner stamp) lgtm

[philipj_slow, 2014-10-24 11:31:59]

The CQ bit was checked by philipj@opera.com

[commit-bot: I haz the power, 2014-10-24 11:32:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/675963002/1

[commit-bot: I haz the power, 2014-10-24 12:15:46]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-24 12:16:31]

Patchset 1 (id:??) landed as
https://crrev.com/1694f0d39e4846fbe53ea7f33943502bdd015932
Cr-Commit-Position: refs/heads/master@{#301083}