Use RAII for write libpng structs.

Use RAII for write libpng structs.

Previously RAII was only being used for read libpng structs.

These changes were split from the patch at
http://codereview.chromium.org/9496004

TEST=--gtest_filter=PNGCodec*

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=130358

[Francois, 2012-04-02 09:16:57]

Hi guys, please review this, another small refactoring patch that was stripped
from http://codereview.chromium.org/9496004 (Support for interlaced PNGs (in
gfx::PNGCodec)). Thanks!

[sky, 2012-04-02 15:35:01]

LGTM. In the future pick just one reviewer.

https://chromiumcodereview.appspot.com/9959061/diff/1/ui/gfx/codec/png_codec.cc
File ui/gfx/codec/png_codec.cc (right):

https://chromiumcodereview.appspot.com/9959061/diff/1/ui/gfx/codec/png_codec....
ui/gfx/codec/png_codec.cc:379: };
DISALLOW_COPY_AND_ASSIGN

[Francois, 2012-04-03 09:01:23]

On 2012/04/02 15:35:01, sky wrote:
> LGTM. In the future pick just one reviewer.
> 
>
https://chromiumcodereview.appspot.com/9959061/diff/1/ui/gfx/codec/png_codec.cc
> File ui/gfx/codec/png_codec.cc (right):
> 
>
https://chromiumcodereview.appspot.com/9959061/diff/1/ui/gfx/codec/png_codec....
> ui/gfx/codec/png_codec.cc:379: };
> DISALLOW_COPY_AND_ASSIGN

OK I will. Comment addressed and committing. Thanks!

[commit-bot: I haz the power, 2012-04-03 09:01:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/francoisk777@gmail.com/9959061/4001

[commit-bot: I haz the power, 2012-04-03 12:04:29]

Change committed as 130358

[Nico, 2016-12-14 20:15:12]

thakis@chromium.org changed reviewers:
+ thakis@chromium.org

[Nico, 2016-12-14 20:15:13]

It's been a few years, but this introduced a subtle (and harmless, but
detectable by tools) bug: https://codereview.chromium.org/2576823002/#msg6

Just in case you're using this RAII class elsewhere :-)