We don't want to make this a pure interface, as it makes all implementors

We don't want to make this a pure interface, as it makes all implementors
bear the burden of implementing what will be all exactly the same methods.
They just want to provide the information in differing ways.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12239 91177308-0d34-0410-b5e6-96231b3b80d8