[skottie] Prevent renderstorm
[skottie] Prevent renderstorm

When we called editor.set(), it would call the onChange event for
every difference, which would call render many times...
eventually running the browser out of memory.

This stops that especially when we upload a new JSON file for
rendering.

Bug: skia:
Change-Id: I946659cbe8340f809affe8c2cf613c72939ac943
Reviewed-on: https://skia-review.googlesource.com/156222
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Commit-Queue: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot