[skjson] Unescape strings

Bug: skia:
Change-Id: Ie40f498c87cb57ee59c9bea41b1ff3d81a9b5858
Reviewed-on: https://skia-review.googlesource.com/c/167240
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed