Add "Chrome Helper" to taskkill script on macos

tools/task_kill.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 #
 
 # A script to kill hanging processs. The tool will return non-zero if any
 # process was actually found.
 #
@@ skipping 28 matching lines @@
     'content_shell': 'content_shell',
     'dart': 'dart',
     'firefox': 'firefox.exe',
     'git': 'git',
     'svn': 'svn',
     'fletch': 'fletch',
     'fletch-vm': 'fletch-vm',
   },
   'macos': {
     'chrome': 'Chrome',
+    'chrome_helper': 'Chrome Helper',
     'content_shell': 'Content Shell',
     'dart': 'dart',
     'firefox': 'firefox',
     'safari': 'Safari',
     'git': 'git',
     'svn': 'svn',
     'fletch': 'fletch',
     'fletch-vm': 'fletch-vm',
   }
 }
@@ skipping 144 matching lines @@
     print("Killed pid: %s" % pid)
   if len(pids) == 0:
     print("  No %s processes found." % name)
   return len(pids)
 
 def KillBrowsers():
   status = Kill('firefox')
   # We don't give error on killing chrome. It happens quite often that the
   # browser controller fails in killing chrome, so we silently do it here.
   Kill('chrome')
+  status += Kill('chrome_helper')
   status += Kill('iexplore')
   status += Kill('safari')
   status += Kill('content_shell')
   return status
 
 def KillVCSystems():
   status = Kill('git')
   status += Kill('svn')
   return status
 
@@ skipping 18 matching lines @@
   if options.kill_fletch:
     status += KillFletch()
   if options.kill_vc:
     status += KillVCSystems()
   if options.kill_browsers:
     status += KillBrowsers()
   return status
 
 if __name__ == '__main__':
   sys.exit(Main())