webassembly: prototype accessibility and native input support [Spike]

Qt renders its UI interface to a <canvas>, which prevents the browser from knowing the structure of the application. This means that screen readers won't work, and that mobile browsers will not show the virtual keyboard when text input fields gain focus.

It may be possible to provide this information to the web browser by overlaying invisible html elements on the canvas element.

See http://jsfiddle.net/8osw38wf/ for css prototyping.
 
The CanvasRenderingContext2D.addHitRegion() API seems to cover this use case, but only partially implemented under a flag in Chrome and Firefox. https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/addHitRegion

The Accessibility Object Model (AOM) : https://github.com/WICG/aom