Fix alpha contribution to tonal color.

Also adds a tonal color GM, a grayscale mode to shadowutils GM,
and animated alpha to SampleAndroidShadows.

Bug: skia:
Change-Id: I1dcb5cab7e53ffa7a3bf1a07b6ebfed38df1a9ed
Reviewed-on: https://skia-review.googlesource.com/85002
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
8 files changed