Drop default port number in `http_server.py` and `shell.py`.

mojo/devtools/common/devtoolslib/http_server.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 atexit
 import datetime
 import email.utils
 import errno
 import hashlib
 import logging
@@ skipping 189 matching lines @@
       pass
 
     def __del__(self):
       if self.gzipped_file_name:
         os.remove(self.gzipped_file_name)
 
   RequestHandler.protocol_version = 'HTTP/1.1'
   return RequestHandler
 
 
-def start_http_server(mappings, host_port=0):
+def start_http_server(mappings, host_port):
   """Starts an http server serving files from |local_dir_path| on |host_port|.
 
   Args:
     mappings: List of tuples (prefix, local_base_path_list) mapping URLs that
         start with |prefix| to one or more local directories enumerated in
         |local_base_path_list|. The prefixes should skip the leading slash.
         The first matching prefix and the first location that contains the
         requested file will be used each time.
     host_port: Port on the host machine to run the server on. Pass 0 to use a
         system-assigned port.
@@ skipping 23 matching lines @@
             'lsof -i :%d | grep LISTEN | awk \'{print $2}\' | xargs kill -9'
             % host_port)
       else:
         find_cmd = 'fuser %d/tcp' % host_port
         terminate_cmd = 'fuser -k %d/tcp' % host_port
       print ('  Run `%s` to find out which process is using the port;'
              % find_cmd)
       print ('  or `%s` terminate it.' % terminate_cmd)
     print '---'
     raise