Explicitly require rooted device in `mojo_test`.

mojo/devtools/common/devtoolslib/android_shell.py

Index: mojo/devtools/common/devtoolslib/android_shell.py
diff --git a/mojo/devtools/common/devtoolslib/android_shell.py b/mojo/devtools/common/devtoolslib/android_shell.py
index c3bed337caeb7a60829fbc45be71c563cdf30a12..a4a7d16db7261e650c0c776564dc35a6655e537b 100644
--- a/mojo/devtools/common/devtoolslib/android_shell.py
+++ b/mojo/devtools/common/devtoolslib/android_shell.py
@@ -199,7 +199,7 @@ class AndroidShell(Shell):
     return len(subprocess.check_output(self._adb_command([
         'shell', 'pm', 'list', 'packages', _MOJO_SHELL_PACKAGE_NAME]))) > 0
 
-  def check_device(self):
+  def check_device(self, require_root=False):
     """Verifies if the device configuration allows adb to run.
 
     If a target device was indicated in the constructor, it checks that the
@@ -234,6 +234,9 @@ class AndroidShell(Shell):
     if not device_list[0].endswith('device'):
       return False, 'Connected device is not available.'
 
+    if require_root and not self._run_adb_as_root():
+      return False, 'Cannot run on an unrooted device.'
+
     return True, None
 
   def install_apk(self, shell_apk_path):