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

mojo/devtools/common/devtoolslib/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.
 
 
 class Shell(object):
   """Represents an abstract Mojo shell."""
 
-  def serve_local_directories(self, mappings, port=0, reuse_servers=False):
+  def serve_local_directories(self, mappings, port, reuse_servers=False):
     """Serves the content of the local (host) directories, making it available
     to the shell under the url returned by the function.
 
     The server will run on a separate thread until the program terminates. The
     call returns immediately.
 
     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.
@@ skipping 39 matching lines @@
           terminated
 
     Returns:
       A tuple of (return_code, output, did_time_out). |return_code| is the exit
       code returned by the shell or None if the exit code cannot be retrieved.
       |output| is the stdout mingled with the stderr produced by the shell.
       |did_time_out| is True iff the shell was terminated because it exceeded
       the |timeout| and False otherwise.
     """
     raise NotImplementedError()