[skottie] Eliminate some temp SkString allocations

Use the SkJSON conversion idiom instead of ParseDefault<SkString>.

Change-Id: Ieeadb86891602eaef2ecf5b68a4eb17b4897e8f7
Reviewed-on: https://skia-review.googlesource.com/147103
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed