Roll back the changes I made in r193907 which created a new Frame
pure virtual base class and made StackFrame a subclass of that.  As
I started to build on top of that arrangement today, I found that it
wasn't working out like I intended.  Instead I'll try sticking with
the single StackFrame class -- there's too much code duplication to
make a more complicated class hierarchy sensible I think.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@193983 91177308-0d34-0410-b5e6-96231b3b80d8