Fix ComposeOneFragmentProcessor coverage as alpha optimization.

It should only be advertised if the child also advertises it.

Change-Id: I698213c9562d710dff45f0622d50eacc41e29af5
Reviewed-on: https://skia-review.googlesource.com/8811
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed