* Remove time
* Remove rand
* Remove array buffers
* Remove more code
* Remove more image decoding code
* Remove more code
* Remove old public API
* Remove more old public headers
* Remove layout test support
* Remove WebPrivateOwnPtr
* Remove WebString
* Remove worker pool
Currently we run some tasks on the UI thread that shouldn't block the frame,
such as decoding images. This patch introduces a background thread on which we
can run these tasks.