Fix alpha computation for specular lighting filter (GPU path).
Change lighting GM background to show blending.

NOTE:  This will require new results for the lighting GM.

Review URL: https://codereview.appspot.com/6812050

git-svn-id: http://skia.googlecode.com/svn/trunk@6181 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed