Add ServeLocalDirectory to the shell abstraction.

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 hashlib
 import logging
 import math
@@ skipping 108 matching lines @@
       return os.path.join(base_path, os.path.relpath(path_from_current))
 
     def log_message(self, *_):
       """Override the base class method to disable logging."""
       pass
 
   RequestHandler.protocol_version = 'HTTP/1.1'
   return RequestHandler
 
 
-def StartHttpServer(path):
-  """Starts an http server serving files from |path| on random
-  (system-allocated) port. Returns the server address.
+def StartHttpServer(local_dir_path, host_port=0):
+  """Starts an http server serving files from |path| on |host_port|. Pass 0
+  as |host_port| to use a system-allocated port.
+
+  Returns:
+    Tuple of the server address and the port on which it runs.
   """
-  assert path
-  httpd = _SilentTCPServer(('127.0.0.1', 0), _GetHandlerClassForPath(path))
+  assert local_dir_path
+  httpd = _SilentTCPServer(('127.0.0.1', host_port),
+                           _GetHandlerClassForPath(local_dir_path))
   atexit.register(httpd.shutdown)
 
   http_thread = threading.Thread(target=httpd.serve_forever)
   http_thread.daemon = True
   http_thread.start()
   return httpd.server_address