UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:49.0) Gecko/20100101 Firefox/49.0

Steps to reproduce the problem:
Call createImageBitmap( OffscreenCanvas )

What is the expected behavior?
OffscreenCanvas is a member of CanvasImageSource and
CanvasImageSource is a subset of ImageBitmapSource, so it should work.

What went wrong?
TypeError: Failed to execute 'createImageBitmap' on 'Window': The provided value is not of type '(HTMLImageElement or HTMLVideoElement or HTMLCanvasElement or Blob or ImageData or ImageBitmap)'

Did this work before? No 

Chrome version: 55.0.2853.0  Channel: dev
OS Version: 
Flash Version: