[whatwg] Canvas in Workers

[Gregg Tavares (社用)]

discussion seems to have died down here but I'd like to bring up another
issue

In WebGL land we have creation attributes on the drawingbuffer made for a
canvas. Example

    gl = canvas.getContext("webgl", { preserveDrawingBuffer: false });

We're working out the details on how to set those options for the case
where we have 1 context and multiple canvases.

The particular option above would apparently be a huge perf win for canvas
2d for mobile. Which suggests that whatever API is decided on it would be
nice if it worked for both APIs the same.