There are quite a few steps between a ReadableStream being created and
its controller being set. If GC occurs between those points, we will
have an empty Optional in ReadableStream::visit_edges. Seen on YouTube.
This is not documented yet, but the preferred style is getting both
upfront instead of inlining various kinds of calls in places that use
the realm and vm.
Note that as of this commit, there aren't any such throwers, and the
call site in Heap::allocate will drop exceptions on the floor. This
commit only serves to change the declaration of the overrides, make sure
they return an empty value, and to propagate OOM errors frm their base
initialize invocations.
This needs to happen before prototype/constructor intitialization can be
made lazy. Otherwise, GC could run during the C++ constructor and try to
collect the object currently being created.
These classes only needed Window to get at its realm. Pass a realm
directly to construct Crypto, Encoding, HRT, IntersectionObserver,
NavigationTiming, Page, RequestIdleCallback, Selection, Streams, URL,
and XML classes.
