Never try to use root to run the mojo tools.

mojo/devtools/common/devtoolslib/shell_arguments.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.
 
 """Produces configured shell abstractions.
 
 This module knows how to produce a configured shell abstraction based on
 shell_config.ShellConfig.
 """
 
@@ skipping 180 matching lines @@
     |shell_args| is updated list of shell arguments.
 
   Throws:
     ShellConfigurationException if shell abstraction could not be configured.
   """
   if shell_config.android:
     shell = AndroidShell(shell_config.adb_path, shell_config.target_device,
                          logcat_tags=shell_config.logcat_tags,
                          verbose=shell_config.verbose)
 
-    device_status, error = shell.check_device(
-        require_root=shell_config.require_root)
+    device_status, error = shell.check_device()
     if not device_status:
       raise ShellConfigurationException('Device check failed: ' + error)
     if shell_config.shell_path:
       shell.install_apk(shell_config.shell_path)
   else:
     if not shell_config.shell_path:
       raise ShellConfigurationException('Can not run without a shell binary. '
                                         'Please pass --shell-path.')
     shell = LinuxShell(shell_config.shell_path)
     if shell_config.use_osmesa:
@@ skipping 18 matching lines @@
       shell_args = append_to_argument(shell_args, '--content-handlers=',
                                       '%s,%s' % (mime_type,
                                                  content_handler_url))
 
   for dev_server_config in shell_config.dev_servers:
     shell_args = _configure_dev_server(shell, shell_args, dev_server_config,
                                        shell_config.reuse_servers,
                                        shell_config.verbose)
 
   return shell, shell_args