This should let getTypeName() and serialization work even
when deserialization factories haven't been registered.
I've made getTypeName() pure virtual like getFactory(),
and moved all the overrides into SK_FLATTENABLE_HOOKS,
cleaning up all the various ways we've done it before.
All the subclasses override getTypeName() and getFactory()
privately, so there should be no need to document them?
Change-Id: I723cb20099d250c2f2a10be266e3aacc6a061937
Reviewed-on: https://skia-review.googlesource.com/c/163543
Reviewed-by: Cary Clark <caryclark@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
4fee323522