Enable Checkstyle presubmit hook for support lib.

Bug: 31494824
Test: Manually tested by modifying a java file and trying to upload.
Change-Id: I1923f49695d3aadf8ed6d31b82f3b7cb56c18d7f

diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
index eb6f5b4..d628507 100644
--- a/PREUPLOAD.cfg
+++ b/PREUPLOAD.cfg

@@ -1,3 +1,6 @@
+[Hook Scripts]
+checkstyle_hook = ../../development/tools/checkstyle/checkstyle.py --sha ${PREUPLOAD_COMMIT}
+
 [Builtin Hooks]
 commit_msg_bug_field = true
 commit_msg_changeid_field = true