Remove unused fields.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186791 91177308-0d34-0410-b5e6-96231b3b80d8
Handle replacement into a position past the original member.

We were incorrectly computing where to insert a member if it was replacing
a previous member that was before the insert point.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186792 91177308-0d34-0410-b5e6-96231b3b80d8