For OffscreenCanvas we need a way for a Worker to draw once per composited frame.
I suggest we create DedicatedWorkerGlobalScope.requestAnimationFrame(callback) that works similarly to Window.requestAnimationFrame. To reduce latency for applications such as VR, I'd like to run the callback after vsync and let the compositor wait for some implementation-defined amount of time for the callback to complete before compositing the frame; this will give the callback a chance to finish rendering and get the results composited before the next vsync. If the callback runs too long its updates will be applied to some later frame. I suggest we later extend this for worker-based control of CSS transforms etc (i.e. "CompositorWorker"). Rob -- lbir ye,ea yer.tnietoehr rdn rdsme,anea lurpr edna e hnysnenh hhe uresyf toD selthor stor edna siewaoeodm or v sstvr esBa kbvted,t rdsme,aoreseoouoto o l euetiuruewFa kbn e hnystoivateweh uresyf tulsa rehr rdm or rnea lurpr .a war hsrer holsa rodvted,t nenh hneireseoouot.tniesiewaoeivatewt sstvr esn
