Revert incorrect change to GrCoverageSetOp test factory

Change-Id: I7d2c9f4e5c2cded2eb06b9a18b73700726103f15
Reviewed-on: https://skia-review.googlesource.com/11292
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed