Allow conversion from non-opaque to opaque [chrome/m57]

BUG:683787

Change-Id: I1b78cc8d1b5d3917a2a952da036b93022e99e053
Reviewed-on: https://skia-review.googlesource.com/7374
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
(cherry picked from commit bfe8dca7dfdd9cafbccba0a637f2fcd58c7a54fb)
Reviewed-on: https://skia-review.googlesource.com/7402
1 file changed