These are treated differently as the interface members are placed on the
object itself, not its prototype.
As the object itself still needs to be hand-written code, and we can no
longer fully hide the gnarly generated code in the prototype object,
these now generate a 'mixin' class that is added to the actual object
through inheritance.
https://webidl.spec.whatwg.org/#Global
The Window object is massive, so let's do the conversion to IDL step
by step. First up: getting rid of the manual constructor and prototype
definitions, which can be generated from an empty `interface Window`.
The condition for checking if there was already a response in recursive
fetch was accidentally flipped, always causing a null deref.
This made redirects crash for example.
The spec states to only try to close the session *if* it exists. This
situation can occur when closing a session after a Close Window command,
as the session will be closed automatically if it was the last window.
These steps now have more than one caller; specifically, they may be
called from the Delete Session and Close Window endpoints. The session
was only removed from the active session map for the former endpoint.
Instead, let's more accurately handle removing the session where the
spec tells us to, so that all callers properly perform this step.
When some WebDriver spec steps are implemented a bit more literally, we
will end up in a situation where we remove a session from its client's
active session map, but still have more steps to perform. Currently,
when we remove the session, it is immediately destroyed because it is
stored in an OwnPtr. Instead, we can store it as a RefPtr, which will
let the caller to such steps keep the session alive until the subsequent
steps are complete.
While here, this also changes the storage of active sessions to a
HashMap, as all lookups into it are currently a linear search.
