Optimize some alpha blending modes.

- Inline the component calculation helpers.
- Reorder the computation in plus_modeproc.

This doubles the performance of plus_modeproc.

Review URL: http://codereview.appspot.com/88084


git-svn-id: http://skia.googlecode.com/svn/trunk@250 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed