add json dump to pathops unittest

./out/skia/pathops_unittest -J dump.json
will write all Op tests to a JSON file. Since this
will run single threaded, this can take a while,
and generates a 500M file.
A reasonable subset is
./out/skia/pathops_unittest -J dump.json -m PathOpsOp$
around 275K.

This is in service of pathkit.

R=kjlubick@google.com

Bug: skia:
Change-Id: I7e0771639e29755c00036f335a531403044d9d30
Reviewed-on: https://skia-review.googlesource.com/145737
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
4 files changed