Added methods for toggling clip viz, overdraw viz, gpu bound viz.
methods for getting number of commands, toggling command visibility and deleting commands.
Added method for writing out json command list.
bound methods with emscrpiten and connected up to buttons in barebones interface to prove they're working.
Bug: skia:
Change-Id: I3f733b13db00ce5d14b1b5170de8fb66102c8b14
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/199938
Commit-Queue: Nathaniel Nifong <nifong@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
