graphics_*: mark as python3 converted.

BUG=b:201842108
TEST=visual inspection

Change-Id: Icbd951df463fa678f3266b2c7eeef9fdd8567191
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/3201052
Auto-Submit: Ilja H. Friedel <[email protected]>
Tested-by: Ilja H. Friedel <[email protected]>
Reviewed-by: Po-Hsien Wang <[email protected]>
Commit-Queue: Po-Hsien Wang <[email protected]>
diff --git a/server/site_tests/graphics_MultipleDisplays/graphics_MultipleDisplays.py b/server/site_tests/graphics_MultipleDisplays/graphics_MultipleDisplays.py
index 37d86ee..49ad538 100644
--- a/server/site_tests/graphics_MultipleDisplays/graphics_MultipleDisplays.py
+++ b/server/site_tests/graphics_MultipleDisplays/graphics_MultipleDisplays.py
@@ -1,3 +1,4 @@
+# Lint as: python2, python3
 # Copyright 2018 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.