Onscreen<->offscreen transition is broken

[Cyberax]

I've been debugging onscreen/offscreen transitions on Android for the last couple of days, and I believe the current way they're handled is broken fundamentally.

The root reason: it's possible (and easy!) to crash Dawn by racing the JavaScript rendering with the UI thread. In my app, we have several wgpu contexts in a virtualized list and inside tabs, so we quite frequently exercise the onscreen/offscreen transitions, so our app crashes within seconds on Android. And to add even more fun, we often resize our views dynamically.

I was able to keep the app stable by spamming the rendering code with makeshift rendering barriers, but I'm thinking about a more permanent fix. My plan right now:

1. Use "epoch counter" in GPUTexture and other derived objects. They'll have a reference to an "epoch object" that is invalidated the moment a surface gets destroyed (when Android calls onSurfaceTextureDestroyed/surfaceDestroyed). Each method of the GPUTexture gets wrapped in an "epoch guard" that will immediately throw a JS exception once the surface goes away.
2. The onscreen/offscreen transition will also invalidate the texture, causing any concurrent JS rendering to fail.
3. Surface (haha) the paint event to the React world, so that rn-wgpu can request JS to make sure the current rendering is up-to-date. This is a departure from the way wgpu is handled on the web, unfortunately, but I think it's unavoidable.
4. Resize will be handled just as an offscreen/onscreen transition: change the epoch to force any rendering code to fail fast, then request a repaint.

I think this will work reasonably well, but I'm worried about getting bad frames displayed during transitions, resulting in subpar experience. Alternatively, we can always render to an offscreen canvas?

I'd love to discuss this to get some feedback/ideas, but I'm not sure this is the best forum for this.