use SkImageInfo directly, instead of convert to Config

BUG=
R=scroggo@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/128953003

git-svn-id: http://skia.googlecode.com/svn/trunk@12977 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed