Revert of Properly set alpha type in webp decode.

Revert of Properly set alpha type in webp decode. (https://codereview.chromium.org/223893002/)

Reason for revert:
Breaks ImageDecoding tests on several platforms.

Original issue's description:
> Properly set alpha type in webp decode.
> 
> Also use the newer setConfig function.
> 
> Add a test to confirm that we set the alpha type properly.
> 
> Add some images with alpha for testing. (These images are also beneficial for the compare_unpremul test, which was previously not meaningful on 100% opaque images.)
> 
> All of the added images are in the public domain. They were taken from https://developers.google.com/speed/webp/gallery2:
> 
> yellow_rose:
> "Free Stock Photo in High Resolution - Yellow Rose 3 - Flowers"
> Image Author: Jon Sullivan
> This file is in the public domain.
> http://www.public-domain-photos.com/free-stock-photos-4/flowers/yellow-rose-3.jpg
> 
> baby_tux:
> "baby tux for my user page"
> Image Author: Fizyplankton
> This file is in the public domain.
> http://www.minecraftwiki.net/images/8/85/Fizyplankton.png
> 
> NOTRY=true
> 
> Committed: http://code.google.com/p/skia/source/detail?r=14054

TBR=halcanary@google.com
NOTREECHECKS=true
NOTRY=true

Committed: http://code.google.com/p/skia/source/detail?r=14055

[scroggo, 2014-04-03 21:46:52]

Created Revert of Properly set alpha type in webp decode.

[commit-bot: I haz the power, 2014-04-03 21:47:02]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/scroggo@google.com/223903008/1

[commit-bot: I haz the power, 2014-04-03 21:47:21]

Change committed as 14055