Never try to use root to run the mojo tools.

mojo/devtools/common/devtoolslib/shell_config.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.
 
 """Configuration for the shell abstraction.
 
 This module declares ShellConfig and knows how to compute it from command-line
 arguments, applying any default paths inferred from the checkout, configuration
 file, etc.
 """
@@ skipping 19 matching lines @@
     self.map_origin_list = []
     self.dev_servers = []
     self.reuse_servers = False
     self.content_handlers = dict()
     self.verbose = None
 
     # Android-only.
     self.adb_path = None
     self.target_device = None
     self.logcat_tags = None
-    self.require_root = False
 
     # Desktop-only.
     self.use_osmesa = None
 
 
 class DevServerConfig(object):
   """Configuration for a development server running on a host and available to
   the shell.
   """
   def __init__(self):
@@ skipping 161 matching lines @@
 
     if 'content_handlers' in config:
       try:
         for (mime_type,
              content_handler_url) in config['content_handlers'].iteritems():
           shell_config.content_handlers[mime_type] = content_handler_url
       except (ValueError, KeyError):
         raise ShellConfigurationException('Failed to parse content_handlers in '
                                           'the config file.')
   return shell_config