This is not to the specification, but as the FIXME comment for the
function states, we need it to be able to properly interface with the
FileAPI spcification, which seems to have not been updated to the non
promise based API.
This algorithm is used by ReadableStreamDefaultReader to read all bytes
from a given stream. Currently the algorithm used is somewhat naive as
it is recursive, but given the initial use of this reader, it should not
be a problem.
