add bench to time relative gain for convexity

Bug: skia:
Change-Id: I5bd0194a49c74a8e47a210ff06ef4406ecb3bc4c
Reviewed-on: https://skia-review.googlesource.com/c/175585
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed