Adjust canFilterMaskGPU to only reject small rect blurs

Change-Id: Iabcbbac2fc1ff8bcfd87bd774f81cdb4b960daa7
Reviewed-on: https://skia-review.googlesource.com/147560
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed