Canvas rendering context should not be tied to PlatformLayer Currently CanvasRenderingContext "draws to" PlatformLayer, i.e. has CanvasRenderingContext::platformLayer(). This does not work for UI-side compositing, as we do not want the WebGL graphics context need CALayer in the UI process. Instead there should be some sort of abstraction that can be used in conjunction with GraphicsLayer contents property, so that what CanvasRenderingContext draws can be shown as GraphicsLayer contents.
Created attachment 444245 [details] Patch
Created attachment 444380 [details] Patch
Created attachment 444381 [details] Patch
Currently implemented as part of the parent patch in bug 231009