SkJson

For now this is only wired to a bench and a couple of tests.

Local numbers, for a ~500KB BM "compressed" json:

    micros   	bench
   2456.54  	json_rapidjson	nonrendering
   1192.38  	json_skjson	nonrendering


Change-Id: I7b3514f84c7c525d1787722c43ad6095e3692563
Reviewed-on: https://skia-review.googlesource.com/127622
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
8 files changed