[skjson] Size-constrained input API

Pass an explicit input size instead of requiring a C string.

Thanks to mtklein's clever trick, this has no measurable perf impact.

Change-Id: I64f210a9f653a78b05ab6b58fa34479504aa35ff
Reviewed-on: https://skia-review.googlesource.com/134940
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
5 files changed