Extend the StartPassTimer and StopPassTimer functions so that the

Extend the StartPassTimer and StopPassTimer functions so that the
code that stops the timer doesn't have to search to find the timer
object before it stops the timer. This avoids a lock acquisition
and a few other things done with the timer running.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82949 91177308-0d34-0410-b5e6-96231b3b80d8