[mesh2d demo] Updated to latest API

The buffer factories now live in CanvasRenderingContext2D:
https://github.com/fserb/canvas2D/blob/master/spec/mesh2d.md#mesh2d-api

Change-Id: I9d20ed5b74b283a5f2486c57657de466d6a39d9b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/802876
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: Florin Malita <fmalita@chromium.org>
Reviewed-by: John Stiles <johnstiles@google.com>
1 file changed