One side effect is that the SkShader's (or implicit shader's) fragment processor is responsible for the transition from an unpremul paint color to a premul color.
Review URL: https://codereview.chromium.org/1348583002
The new FP is used to implement SkXM::Mode color filters and SkXM::Mode image filters. Also, these now support all advanced SkXM::Mode xfermodes.
Review URL: https://codereview.chromium.org/1334293003