don't compose with (forced) opaque colors

Bug: skia:
Change-Id: Ic5ea706430b4698e7e937a0cc424ec29b0d8da10
Reviewed-on: https://skia-review.googlesource.com/22029
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed