Derive Debug on some of the public types
Derive Debug on some of the public types

Some of the types already have had working Debug implementations (or
derives) available in all the OS-specific backends; but for some reason
they were not exposed on the (portable) API types... Let's change that.

Note that this doesn't cover all of the public types -- some would
actually need Debug implementations to be newly introduced for all the
OS-specific backends, which would be much more involved than just
exposing the existing ones...

servo/ipc-channel