Add another metric for startup delay -- run to breakpoint, which measures the time from issuing

the run command till the first breakpoint hit.  Example:

 $ ./dotest.py -v +b -n -x '-F Driver::MainLoop()' -p TestStartupDelays.py
1: test_startup_delay (TestStartupDelays.StartupDelaysBench)
   Test start up delays creating a target and setting a breakpoint. ... 
lldb startup delay (create fresh target) benchmark: Avg: 0.124496 (Laps: 30, Total Elapsed Time: 3.734883)
lldb startup delay (set first breakpoint) benchmark: Avg: 0.220828 (Laps: 30, Total Elapsed Time: 6.624847)
lldb startup delay (run to breakpoint) benchmark: Avg: 0.478159 (Laps: 30, Total Elapsed Time: 14.344774)
ok

llvm-svn: 142993