Allow to set a fixed port for the development server.

mojo/devtools/common/devtoolslib/shell_arguments.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.
 
 """Produces configured shell abstractions.
 
 This module knows how to produce a configured shell abstraction based on
 shell_config.ShellConfig.
 """
 
@@ skipping 139 matching lines @@
 
   Args:
     shell: The shell that is being configured.
     shell_arguments: Current list of shell arguments.
     dev_server_config: Instance of shell_config.DevServerConfig describing the
         dev server to be set up.
 
   Returns:
     The updated argument list.
   """
-  server_url = shell.serve_local_directories(dev_server_config.mappings)
+  port = dev_server_config.port if dev_server_config.port else 0
+  server_url = shell.serve_local_directories(dev_server_config.mappings,
+                                             port=port)
   shell_args.append('--map-origin=%s=%s' % (dev_server_config.host, server_url))
   print "Configured %s locally at %s to serve:" % (dev_server_config.host,
                                                    server_url)
   for mapping_prefix, mapping_path in dev_server_config.mappings:
     print "  /%s -> %s" % (mapping_prefix, mapping_path)
   return shell_args
 
 
 def get_shell(shell_config, shell_args):
   """
@@ skipping 48 matching lines @@
     for (mime_type,
          content_handler_url) in shell_config.content_handlers.iteritems():
       shell_args = append_to_argument(shell_args, '--content-handlers=',
                                       '%s,%s' % (mime_type,
                                                  content_handler_url))
 
   for dev_server_config in shell_config.dev_servers:
     shell_args = _configure_dev_server(shell, shell_args, dev_server_config)
 
   return shell, shell_args