Webgl support in web worker

[miktoki]

#102 mentions support for running tfjs on a web worker, which is currently supported, but only for the cpu backend. Lack off browser support for offscreencanvas was quoted as a key reason why it has not yet been looked into.
Having webgl+offscreencanvas support on tfjs would make it a lot more usable in realtime applications.
As of now (April 2019), offscreen canvas is supported by 61% of global users (only chrome). Given that there is some offscreencanvas support, is this something you plan to implement?

My understanding of webgl and the challenges with adding support for this on a worker is limited, but what would need to be done to make tfjs work with gpu on a worker?

[tafsiri]

@miktoki We are planning on working on this, there is a WIP PR here tensorflow/tfjs-core#1221, but we anticipate having bandwidth to work on this later in this quarter. I'm going to close this issue in favor of keeping the discussion going in #102 and tensorflow/tfjs-core#1221