In all the call sites that are in this PR, the caller already has a statically typed version of the tree that it can use to pass to these methods.

For example here:
https://github.com/lampepfl/dotty/pull/117/files#diff-374479fca6aeeda64b2b850c4c611cc5R267
the identifier `tree` can be rebound in the pattern so that its static type becomes `CaseDef`.