Backout rev 0c9ff69d4263 to re-land with proper credit. Bug 904723, no_r=me.
Backout rev b221cb63e559 to re-land with proper credit. Bug 904723, no_r=me.
Bug 904723, part 3 - Implement Array.from. r=till. Thanks also to André Bargull for his very close review of this code.
Bug 904723, part 4 - In Array.from, only fetch the @@iterator property once. r=till. DONTBUILD.