color-correct patch

Key work is to correctly convert SkColor corners into linear floats,
then interpolate, then (correctly) convert back to SkColors.

Bug: skia:6659
Change-Id: Iaf0ab842d7a4f8f3481e609903cec83814e5a749
Reviewed-on: https://skia-review.googlesource.com/17533
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
6 files changed