Summary:
1. The base class descriptor was removed, this was given that we have chained descriptor there is no need for this anymore
2. The Base interface node descriptor no longer has a mutable list based api. You simply return a list. The mutable list based api was specifically to allow chaining and this quirk is isoltated to the chained descriptor
3. AbstractChainedDescriptor and ChainedDescriptor were merged
Reviewed By: lblasa
Differential Revision: D39496073
fbshipit-source-id: fb3ec629ec3b27f587bdbd0b323624a4bc4ebea3
2090120cda