Loading of data is extremely slow in web on Chrome

[jleibs]

Repro is relatively straight forward with even simple demos like car demo.

Happens on both chrome and edge browsers, but not on firefox.

Symptom is that new messages arrive at a rate of 2/sec.

You can see this happening in the profile view in chrome:

I don't know enough about the web task worker model to understand why these get scheduled so infrequently or why the task waits for ~15 ms before starting the deserialization function.

[emilk]

What Jeremy has found is that the render task starves the websocket task.

A potential fix is to replace egui_ctx.request_repaint with egui_ctx.request_repaint_after(10ms) when there are messages to process.

[jleibs]

The call to repaint from within the websocket decode_log_msg handler seems to be part of the problem. As suggested, request_repaint_after dramatically improves the performance. However, this is somewhat broken on web and can leave us in a situation where the next render never happens (#1607)

[jleibs]

An additional unfortunate finding is that the google-chrome profiler itself further exacerbates the issue.

[teh-cmc]

Would be nice to redo these measurements when #1880 lands