Improve API for contrast blending functions.

This reduces the number of functions and makes the naming and functionality more
coherent.

Bug: 870384
Change-Id: I67586068ddd32463ad72f0f923540ec6d7bdf737
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610486
Commit-Queue: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661702}
16 files changed