fix the visual diff of raster vs gpu -- vertices_80

fix the visual diff of raster vs gpu -- vertices_80. The sw-raster is correct, all images are blurry.
While some images generated by gpu doesn't respect SkPaint's alpha value.

In gpu path, when pass SkPaint's alpha and color to GrPaint by SkPaint2GrPaintNoShader,
either alpha or colors can't not be passed. We can't pass both of them by the API. 
Premultiply paint's alpha to colors's alpha in drawVertices, and pass colors to GrPaint. 
The rendering result will respect colors in drawVertices, and the alpha value set in SkPaint as well.

BUG=skia:2592
Committed: http://code.google.com/p/skia/source/detail?r=14863

[yunchao, 2014-05-22 07:03:16]

PTAL. Thanks!

[bsalomon, 2014-05-22 13:11:36]

lgtm, any tests that need to be added to ignored-tests.txt for rebaselining?

[yunchao, 2014-05-22 13:38:06]

On 2014/05/22 13:11:36, bsalomon wrote:
> lgtm, any tests that need to be added to ignored-tests.txt for rebaselining?

Thanks for your reviewing, Brian. I will add vertices_80 into ignore-tests.txt
before landing.

[yunchao, 2014-05-23 08:03:22]

The CQ bit was checked by yunchao.he@intel.com

[commit-bot: I haz the power, 2014-05-23 08:03:42]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/yunchao.he@intel.com/292943002/20001

[commit-bot: I haz the power, 2014-05-23 08:09:33]

Change committed as 14863