Support dev servers defined in a mojoconfig file.

mojo/devtools/common/mojo_run

 #!/usr/bin/env python
 # Copyright 2014 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 logging
 import sys
 
 from devtoolslib import shell_arguments
@@ skipping 47 matching lines @@
   shell_config.add_shell_arguments(parser)
 
   parser.add_argument('--no-debugger', action="store_true",
                       help='Do not spawn mojo:debugger.')
   parser.add_argument('--window-manager', default=_DEFAULT_WINDOW_MANAGER,
                       help='Window manager app to be mapped as '
                       'mojo:window_manager. By default it is ' +
                       _DEFAULT_WINDOW_MANAGER)
 
   script_args, shell_args = parser.parse_known_args()
-  config = shell_config.get_shell_config(script_args)
 
   try:
+    config = shell_config.get_shell_config(script_args)
     shell, shell_args = shell_arguments.get_shell(config, shell_args)
-  except shell_arguments.ShellConfigurationException as e:
+  except shell_config.ShellConfigurationException as e:
     print e
     return 1
 
   if not script_args.no_debugger:
     if script_args.verbose:
       print 'Spawning mojo:debugger, use `mojo_debug` to inspect the shell.'
       print 'Note that mojo:debugger will prevent the shell from terminating,'
       print '  pass --no-debugger to skip spawning mojo:debugger.'
     shell_args.extend(_configure_debugger(shell))
 
   shell_args = shell_arguments.append_to_argument(shell_args, '--url-mappings=',
                                                   'mojo:window_manager=%s' %
                                                   script_args.window_manager)
 
   if script_args.verbose:
     print "Shell arguments: " + str(shell_args)
 
   shell.run(shell_args)
   return 0
 
 
 if __name__ == "__main__":
   sys.exit(main())