Add content tests to Checkstyle upload hooks.

Make sure to check style for content tests when uploading
a new change there.

This is a partial cherry-pick of ag/6218940 to help with
a downstream merge conflict of ag/939144

Test: None
Change-Id: I1aedc07a05b61649fc4cfa1e256516ec4ea6e2a3
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index 4870b15..ed70cb9 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg
@@ -12,6 +12,7 @@
                       libs/
                       tests/autofillservice/
                       tests/tests/animation/
+                      tests/tests/content/
                       tests/tests/graphics/
                       tests/tests/hardware/
                       tests/tests/print/