Add const.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205013 91177308-0d34-0410-b5e6-96231b3b80d8
Add const to a method I missed in the previous commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205014 91177308-0d34-0410-b5e6-96231b3b80d8