Handling multi-threaded WebGPU

[greggman]

I'm curious if we can think of a way to support multi-threaded WebGPU. Basically I don't want to find that the only way to debug multi-threaded WebGPU is to NOT use this debugger 😅 Or to put another way, I'd be nice to avoid this code becoming obsolete if and when WebGPU supports multi-threading.

I can't really imagine an efficient way to do it though. Could put the capture in a worker and send messages for each cmd, would make debugging slow but at least it would let you capture all the commands in one place. Unfortunately it would also affect timing so race bugs that show up without the debugger might disappear with it.

I suppose another option is to turn this into a devtools extension and have the capture portion be built into the browser. It's nice not to have to wait for all the browser to support something though so if we can manage to get multi-threaded debugging to work from JS alone that would be great!