Revert "Don't assume backing thread shares protocol ID."

This reverts r329891 because the test case is timing out on linux:
http://lab.llvm.org:8011/builders/lldb-x86_64-ubuntu-14.04-cmake/builds/21834

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@329897 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed