[Android] Convert to DeviceUtils versions of IsOnline, HasRoot, and EnableRoot.

tools/android/mempressure.py

Index: tools/android/mempressure.py
diff --git a/tools/android/mempressure.py b/tools/android/mempressure.py
index 82fe2206dfd252bf04f9cd05ceaca8a569f578b0..51c5c8fc9ca415842e90fb3c5e322e2bfc185cd1 100755
--- a/tools/android/mempressure.py
+++ b/tools/android/mempressure.py
@@ -86,7 +86,11 @@ def main(argv):
 
   device = device_utils.DeviceUtils(None)
 
-  device.old_interface.EnableAdbRoot()
+  try:
+    device.EnableRoot()
+  except device_errors.CommandFailedError:
+    # Try to change the flags and start the activity anyway.
+    pass
   flags = flag_changer.FlagChanger(device, package_info.cmdline_file)
   if ENABLE_TEST_INTENTS_FLAG not in flags.Get():
     flags.AddFlags([ENABLE_TEST_INTENTS_FLAG])