We only use nsINamed on runnables for certain kinds of telemetry, and
those kinds of telemetry aren't being gathered on RELEASE_OR_BETA
builds. We effectively make nsINamed::GetName a no-op when we're not
collecting said telemetry. But implementing nsINamed does have a cost:
the vtable of every runnable (and we have hundreds of subclasses of
mozilla::Runnable) will contain pointers for GetName (and extra pointers
for QueryInterface/AddRef/Release), and all those pointers times all
those subclasses adds up quickly. Let's not implement nsINamed when
nsINamed isn't going to be used.
This change saves ~100K of binary size on x86-64 Linux; the savings
should be similar on other 64-bit systems, and ~50K on 32-bit systems.
This enables having a const nsMainThreadPtrHandle<T> member which we want to
ensure doesn't get assigned to, but whose (the `T`'s) non-const methods are
still usable on main thread. Similar to how RefPtr<T> works.
MozReview-Commit-ID: 8CG0MwIZmLc
