diff --git a/mojo/devtools/common/devtoolslib/shell_arguments.py b/mojo/devtools/common/devtoolslib/shell_arguments.py
new file mode 100644
index 0000000..bf70f89
--- /dev/null
+++ b/mojo/devtools/common/devtoolslib/shell_arguments.py
@@ -0,0 +1,65 @@
+# 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.
+
+"""Functions that configure the shell before it is run manipulating its argument
+list."""
+
+import urlparse
+
+_MAP_ORIGIN_PREFIX = '--map-origin='
+# When spinning up servers for local origins, we want to use predictable ports
+# so that caching works between subsequent runs with the same command line.
+_MAP_ORIGIN_BASE_PORT = 31338
+
+
+def _IsMapOrigin(arg):
+  """Returns whether |arg| is a --map-origin argument."""
+  return arg.startswith(_MAP_ORIGIN_PREFIX)
+
+
+def _Split(l, pred):
+  positive = []
+  negative = []
+  for v in l:
+    if pred(v):
+      positive.append(v)
+    else:
+      negative.append(v)
+  return (positive, negative)
+
+
+def _RewriteMapOriginParameter(shell, mapping, device_port):
+  parts = mapping[len(_MAP_ORIGIN_PREFIX):].split('=')
+  if len(parts) != 2:
+    return mapping
+  dest = parts[1]
+  # If the destination is a url, don't map it.
+  if urlparse.urlparse(dest)[0]:
+    return mapping
+  # Assume the destination is a local directory and serve it.
+  localUrl = shell.ServeLocalDirectory(dest, device_port)
+  print 'started server at %s for %s' % (dest, localUrl)
+  return _MAP_ORIGIN_PREFIX + parts[0] + '=' + localUrl
+
+
+def RewriteMapOriginParameters(shell, original_arguments):
+  """Spawns a server for each local destination indicated in a map-origin
+  argument in |original_arguments| and rewrites it to point to the server url.
+  The arguments other than "map-origin" and "map-origin" arguments pointing to
+  web urls are left intact.
+
+  Args:
+    shell: The shell that is being configured.
+    original_arguments: List of arguments to be rewritten.
+
+  Returns:
+    The updated argument list.
+  """
+  map_arguments, other_arguments = _Split(original_arguments, _IsMapOrigin)
+  arguments = other_arguments
+  next_port = _MAP_ORIGIN_BASE_PORT
+  for mapping in sorted(map_arguments):
+    arguments.append(_RewriteMapOriginParameter(shell, mapping, next_port))
+    next_port += 1
+  return arguments
diff --git a/mojo/tools/android_mojo_shell.py b/mojo/tools/android_mojo_shell.py
index 7d015a2..7edad0f 100755
--- a/mojo/tools/android_mojo_shell.py
+++ b/mojo/tools/android_mojo_shell.py
@@ -6,11 +6,11 @@
 import argparse
 import logging
 import sys
-import urlparse
 
 import devtools
 devtools.add_lib_to_path()
 from devtoolslib.android_shell import AndroidShell
+from devtoolslib import shell_arguments
 
 from mopy.config import Config
 from mopy.paths import Paths
@@ -32,41 +32,6 @@
 text/html,mojo:html_viewer,application/javascript,mojo:js_content_handler
 """)
 
-_MAPPING_PREFIX = '--map-origin='
-# When spinning up servers for local origins, we want to use predictable ports
-# so that caching works between subsequent runs with the same command line.
-_MAP_ORIGIN_BASE_PORT = 31338
-
-
-def _IsMapOrigin(arg):
-  """Returns whether |arg| is a --map-origin argument."""
-  return arg.startswith(_MAPPING_PREFIX)
-
-
-def _Split(l, pred):
-  positive = []
-  negative = []
-  for v in l:
-    if pred(v):
-      positive.append(v)
-    else:
-      negative.append(v)
-  return (positive, negative)
-
-
-def _RewriteMapOriginParameter(shell, mapping, device_port):
-  parts = mapping[len(_MAPPING_PREFIX):].split('=')
-  if len(parts) != 2:
-    return mapping
-  dest = parts[1]
-  # If the destination is a url, don't map it.
-  if urlparse.urlparse(dest)[0]:
-    return mapping
-  # Assume the destination is a local directory and serve it.
-  localUrl = shell.ServeLocalDirectory(dest, device_port)
-  print 'started server at %s for %s' % (dest, localUrl)
-  return _MAPPING_PREFIX + parts[0] + '=' + localUrl
-
 
 def main():
   logging.basicConfig()
@@ -99,16 +64,8 @@
   shell.InstallApk(paths.target_mojo_shell_path)
   args.append("--origin=" + launcher_args.origin if launcher_args.origin else
               shell.SetUpLocalOrigin(paths.build_dir))
-
-  # Serve the local destinations indicated in map-origin arguments and rewrite
-  # the arguments to point to server urls.
-  map_parameters, other_parameters = _Split(args, _IsMapOrigin)
-  parameters = other_parameters
-  next_port = _MAP_ORIGIN_BASE_PORT
-  for mapping in sorted(map_parameters):
-    parameters.append(_RewriteMapOriginParameter(shell, mapping, next_port))
-    next_port += 1
-  shell.Run(parameters)
+  args = shell_arguments.RewriteMapOriginParameters(shell, args)
+  shell.Run(args)
   return 0