Fixes for unpremul decode.

Fixes for unpremul decode.

SkImageDecoder_CG.cpp:
If a non opaque bitmap was decoded, and the caller wants
unpremultiplied, unpremultiply the colors.

Always use the RGB colorspace, since the other colorspaces
do not match the desired bitmap format.

ImageDecodingTest:
Allow for a difference of 1 in each color component when comparing
the result of premultiplying the unpremultiplied decode with the
premultiplied decode, since I found an image (in WEBP format) where
the unpremultiplied colors did not compare perfectly in my comparison.

R=reed@google.com

Committed: https://code.google.com/p/skia/source/detail?r=9628

[reed1, 2013-06-14 19:38:20]

lgtm w/ optimization suggestion/question.

https://codereview.chromium.org/17084012/diff/1/src/ports/SkImageDecoder_CG.cpp
File src/ports/SkImageDecoder_CG.cpp (right):

https://codereview.chromium.org/17084012/diff/1/src/ports/SkImageDecoder_CG.c...
src/ports/SkImageDecoder_CG.cpp:55: U8CPU a = SkGetPackedA32(color);
possibly only do this if a is != 0xFF and a != 0 ?

[commit-bot: I haz the power, 2013-06-14 20:37:32]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/scroggo@google.com/17084012/1

[scroggo, 2013-06-14 20:39:52]

Committed patchset #1 manually as r9628 (presubmit successful).