Adds a couple more measures to the benchmarking app

mojo/devtools/common/mojo_benchmark

 #!/usr/bin/env python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Runner for Mojo application benchmarks."""
 
 import argparse
 import logging
 import sys
@@ skipping 18 matching lines @@
     # List of measurements to make.
     'measurements': [
       '<measurement type>/<event category>/<event name>',
     ]
   }
 
 Available measurement types are:
 
   - 'time_until' - time until the first occurence of the targeted event
   - 'avg_duration' - average duration of the targeted event
+  - 'percentile_duration' - value at XXth percentile of the targeted event where
+    XX is from the measurement spec, i.e. .../<event name>/0.XX
 
 |benchmark_list_file| may reference the |target_os| global that will be any of
 ['android', 'linux'], indicating the system on which the benchmarks are to be
 run.
 """
 
 _logger = logging.getLogger()
 
 _BENCHMARK_APP = 'https://core.mojoapps.io/benchmark.mojo'
 _CACHE_SERVICE_URL = 'mojo:url_response_disk_cache'
@@ skipping 110 matching lines @@
                    save_traces=script_args.save_traces)
     _run_benchmark(shell, shell_args, name, app, duration, measurements,
                    cold_start=False, verbose=script_args.verbose,
                    android=script_args.android,
                    save_traces=script_args.save_traces)
 
   return 0 if succeeded else 1
 
 if __name__ == '__main__':
   sys.exit(main())