This is not 100% complete: it lacks support for several kinds of nodes
and supports only a bare handful of builtin functions, but it
demonstrates the core functionality and it should be relatively
straightforward to fill in the missing pieces.
Change-Id: I3058089338e20eebc3da18ac5571801abcaab564
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/331177
Reviewed-by: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
