Fix from: Scott Knight(knightsc@gmail.com):

Use a map rather than a vector to store the objects managed by the shared 
cluster since mostly want this for random lookup, so the map is much faster.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@209010 91177308-0d34-0410-b5e6-96231b3b80d8