[tools/perf] Make --trybot argument required for run_benchmark trybot command

tools/perf/core/trybot_command.py

 # 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.
 
 import argparse
 import os
 import logging
 import re
 import subprocess
 import urllib2
@@ skipping 126 matching lines @@
 
   @classmethod
   def AddCommandLineArgs(cls, parser, environment):
     del environment  # unused
     available_bots = _GetTrybotList(cls._GetBuilderList())
     parser.add_argument('benchmark_name', type=str)
     parser.add_argument(
       '--trybot', choices=available_bots,
       help=('specify which bots to run telemetry benchmarks on. '
             ' Allowed values are:\n'+'\n'.join(available_bots)),
-      metavar='')
+      metavar='', required=True)
 
   def Run(self, options, extra_args=None):
     """Sends a tryjob to a perf trybot.
 
     This creates a branch, telemetry-tryjob, switches to that branch, edits
     the bisect config, commits it, uploads the CL to rietveld, and runs a
     tryjob on the given bot.
     """
     if extra_args is None:
       extra_args = []
@@ skipping 195 matching lines @@
       logging.info('Checked out original branch: %s', original_branchname)
       returncode, out, err = _RunProcess(
           ['git', 'branch', '-D', 'telemetry-tryjob'])
       if returncode:
         logging.error('Could not delete telemetry-tryjob branch. '
                       'Please delete it manually: %s', err)
         return ERROR # pylint: disable=lost-exception
       logging.info('Deleted temp branch: telemetry-tryjob')
     return SUCCESS