Right now, the concrete nsXPConnect implements nsIXPConnect and
nsIThreadJSContextStack separately. I want to migrate the API from the latter
interface to the former, but I can't right now because it means we'd end up
with a duplicated method (getSafeJSContext). Since there's only one concrete
class that implements nsXPConnect, let's just use interface inheritance, which
simplifies the migration.
There are several changes here:
1) Adds some MutableThis methods to Optional, Nullable, and dictionaries to
effectively allow doing a const_cast without knowing the actual type being
templated over. I needed this because I do not in fact know that type in
the relevant code. I'm open to suggestions for a better name for this
method.
2) Adds some operator& to RootedJSValue to make it look more like a JS::Value,
and in particular so I can JS_WrapValue the thing in it.
3) Adds a Slot() method to NonNullLazyRootedObject, just like NonNull has.
4) Adds an operator& to LazyRootedObject to make it look more like JSObject* so
I can JS_WrapObject the thing in it.
5) Implements the actual rewrapping of the arguments into the content compartment.
6) Fixes a small preexisting bug in which we didn't look at named constructors
in getTypesFromDescriptor (this was causing my tests to not compile).
7) Changes Xrays to not enter the content compartment when calling a WebIDL
constructor.
8) Adds some friend API to report things as not being functions.
There are some other uses of ObjectIsNativeWrapper in other scriptable helpers
that are tempting to remove as well, but it's probably just better to wait for
that stuff to just go away. Given that the issue we're running into here is
Window-specific, there's not a pressing need to fix the other stuff.
Right now, it sometimes fills out |desc|, and sometimes just defines the property
on the holder. This can get confusing, so let's refine the semantics here and
describe them in a big comment.
The current setup is just an artifact of how it used to be before I refactored
Xrays. Have it as a virtual trap is more flexible since it allows us to invoke
the right trap by just calling GetXrayTraits(wrapper) from non-templatized code.
