We want to unify local and remote calls for these interfaces.

1. Rename HyperTextAccessible, TableAccessible, TableCellAccessible and ImageAccessible to LocalHyperTextAccessible, LocalTableAccessible, LocalTableCellAccessible and LocalImageAccessible, respectively.
2. Create base classes for HyperTextAccessible, TableAccessible, TableCellAccessible and ImageAccessible with pure virtual methods for the methods called by OS/XPCOM implementations.
3. Have LocalHyperTextAccessible, etc. inherit from the new base HyperTextAccessible, etc, marking appropriate methods as overrides.
4. Remove conditional local/remote code paths for these methods from OS/XPCOM implementations.

Open question: Should we drop HyperTextAccessible as a base and just pull it into Accessible? At least on the web, almost everything is a HyperTextAccessible. There are some exceptions, but we could just handle those with IsHyperText checks.

We probably don't need ImageAccessible as a base either, since it just adds Size() and Position() (not even virtual!) and they just call Bounds().

I think it's going to be more effective for us to unify base classes as we get caching working for things that need it, rather than trying to do all this unificatoin in one push. For example, we'll deal with HyperTextAccessible in bug 1730088.