Add `mojo_run --free-ports` to run servers on system-allocated ports.

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 49 matching lines @@
   if _is_web_url(parts[1]):
     # The destination is a web url, do nothing.
     return mapping
 
   src = parts[0]
   dest = host_destination_functon(shell, parts[1], port, free_host_port)
   return src + '=' + dest
 
 
 def _apply_mappings(shell, original_arguments, map_urls, map_origins,
-                    free_host_ports):
+                    free_ports, free_host_ports):
   """Applies mappings for specified urls and origins. For each local path
   specified as destination a local server will be spawned and the mapping will
   be rewritten accordingly.
 
   Args:
     shell: The shell that is being configured.
     original_arguments: Current list of shell arguments.
     map_urls: List of url mappings, each in the form of
         <url>=<url-or-local-path>.
     map_origins: List of origin mappings, each in the form of
         <origin>=<url-or-local-path>.
+    free_ports: Iff True, run local development servers on system-allocated
+        ports. This defeats any performance benefits from caching.
+    free_host_ports: Only applicable on Android. Iff True, local development
+        servers are run on system-allocated ports, but are still forwarded from
+        fixed ports on the device.
 
   Returns:
     The updated argument list.
   """
-  next_port = _MAPPINGS_BASE_PORT
+  next_port = 0 if free_ports else _MAPPINGS_BASE_PORT
   args = original_arguments
   if map_urls:
     # Sort the mappings to preserve caching regardless of argument order.
     for map_url in sorted(map_urls):
       mapping = _rewrite(map_url, _host_local_url_destination, shell, next_port,
                          free_host_ports)
-      next_port += 1
+      if not free_ports:
+        next_port += 1
       # All url mappings need to be coalesced into one shell argument.
       args = append_to_argument(args, '--url-mappings=', mapping)
 
   if map_origins:
     for map_origin in sorted(map_origins):
       mapping = _rewrite(map_origin, _host_local_origin_destination, shell,
                          next_port, free_host_ports)
-      next_port += 1
+      if not free_ports:
+        next_port += 1
       # Origin mappings are specified as separate, repeated shell arguments.
       args.append('--map-origin=' + mapping)
   return args
 
 
-def configure_local_origin(shell, local_dir, free_host_port):
+def configure_local_origin(shell, local_dir, port, free_host_port):
   """Sets up a local http server to serve files in |local_dir| along with
   device port forwarding if needed.
 
   Returns:
     The list of arguments to be appended to the shell argument list.
   """
 
-  origin_url = shell.serve_local_directory(
-      local_dir, _LOCAL_ORIGIN_PORT, free_host_port)
+  origin_url = shell.serve_local_directory(local_dir, port, free_host_port)
   return ["--origin=" + origin_url]
 
 
 def append_to_argument(arguments, key, value, delimiter=","):
   """Looks for an argument of the form "key=val1,val2" within |arguments| and
   appends |value| to it.
 
   If the argument is not present in |arguments| it is added.
 
   Args:
@@ skipping 81 matching lines @@
   else:
     if not shell_config.shell_path:
       raise ShellConfigurationException('Can not run without a shell binary. '
                                         'Please pass --shell-path.')
     shell = LinuxShell(shell_config.shell_path)
     if shell_config.use_osmesa:
       shell_args.append('--args-for=mojo:native_viewport_service --use-osmesa')
 
   shell_args = _apply_mappings(shell, shell_args, shell_config.map_url_list,
                                shell_config.map_origin_list,
+                               shell_config.free_ports,
                                shell_config.free_host_ports)
 
   if shell_config.origin:
     if _is_web_url(shell_config.origin):
       shell_args.append('--origin=' + shell_config.origin)
     else:
+      local_origin_port = 0 if shell_config.free_ports else _LOCAL_ORIGIN_PORT
       shell_args.extend(configure_local_origin(shell, shell_config.origin,
+                                               local_origin_port,
                                                shell_config.free_host_ports))
 
   if shell_config.content_handlers:
     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,
                                        shell_config.free_host_ports,
                                        shell_config.verbose)
 
   return shell, shell_args