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

mojo/devtools/common/devtoolslib/linux_shell.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 subprocess
 import threading
 import tempfile
 
 from devtoolslib import http_server
 from devtoolslib.shell import Shell
 from devtoolslib.utils import overrides
 
 
 class LinuxShell(Shell):
   """Wrapper around Mojo shell running on Linux.
 
   Args:
     executable_path: path to the shell binary
     command_prefix: optional list of arguments to prepend to the shell command,
         allowing e.g. to run the shell under debugger.
   """
 
   def __init__(self, executable_path, command_prefix=None):
     self.executable_path = executable_path
     self.command_prefix = command_prefix if command_prefix else []
 
   @overrides(Shell)
-  def serve_local_directories(self, mappings, port=0, reuse_servers=False):
+  def serve_local_directories(self, mappings, port, reuse_servers=False):
     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://%s:%d/' % server_address
 
   @overrides(Shell)
   def forward_host_port_to_shell(self, host_port):
@@ skipping 15 matching lines @@
     wait_thread.join(timeout)
 
     did_time_out = False
     if p.poll() is None:
       did_time_out = True
       p.terminate()
       p.poll()
     output_file.seek(0)
     output = output_file.read()
     return p.returncode, output, did_time_out