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

mojo/devtools/common/devtoolslib/android_shell.py

 # 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 atexit
 import hashlib
 import logging
 import os
 import os.path
 import random
@@ skipping 403 matching lines @@
           host_port = self._forward_host_port_to_device(0, device_port)
           print ("Dart observatory available at the host at http://127.0.0.1:%d"
                  % host_port)
 
     logcat_watch_thread = threading.Thread(
         target=_forward_observatories_as_needed)
     logcat_watch_thread.daemon = True
     logcat_watch_thread.start()
 
   @overrides(Shell)
-  def serve_local_directories(self, mappings, port=0, reuse_servers=False):
+  def serve_local_directories(self, mappings, port, reuse_servers=False):
     assert mappings
     if reuse_servers:
       assert port, 'Cannot reuse the server when |port| is 0.'
       server_address = ('127.0.0.1', port)
     else:
       server_address = http_server.start_http_server(mappings, port)
 
     return 'http://127.0.0.1:%d/' % self._forward_device_port_to_host(
         port, server_address[1])
 
@@ skipping 29 matching lines @@
           Results.output = rf.read()
 
     run_thread = threading.Thread(target=do_run)
     run_thread.start()
     run_thread.join(timeout)
 
     if run_thread.is_alive():
       self.stop_shell()
       return None, Results.output, True
     return None, Results.output, False