Fix to lcd blending in ganesh

This fixes the bug where a src color may originally be opaque but after
blending it is no longer opaque. We need to know the opacity after the
blend so this restricts us on which blend modes even work this way.

Bug: skia:
Change-Id: Ib3208887d718e5f25272ed7b0bf44683d04884d7
Reviewed-on: https://skia-review.googlesource.com/17488
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed