Bug 969722 - Part 1: Remove ThreadPoolWorker subclasses for ease of inlining. (r=nmatsakis)
Bug 976848 - Add a 32-bit xorshift to ThreadPoolWorker for thread-local PRNG for workstealing. (r=nmatsakis)
Bug 969722 - Part 2: Inline ForkJoinGetSlice. (r=nmatsakis)
Bug 944353. If we've encountered an error while decoding an image and the main thread has asked to do more decoding of that image before the main thread has acknowledged the error then refuse to decode more. r=seth
Bug 944353. If we've had a decoder error then the image is not usable. r=seth

This matches what RasterImage will do.