mysql_stats: Add deadlock metrics

We might be interested in these deadlock metrics that MySQL collects, to
check whether slowness could be caused by deadlock bugs.

BUG=chromium:699600
TEST=None

Change-Id: I942c67cb048931f058560fbce7a2ee8892bf9711
Reviewed-on: https://chromium-review.googlesource.com/513386
Commit-Ready: Paul Hobbs <phobbs@google.com>
Tested-by: Paul Hobbs <phobbs@google.com>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/site_utils/stats/mysql_stats.py b/site_utils/stats/mysql_stats.py
index d9db90c..9249a59 100755
--- a/site_utils/stats/mysql_stats.py
+++ b/site_utils/stats/mysql_stats.py
@@ -46,6 +46,8 @@
     'connections',
     'Innodb_buffer_pool_read_requests',
     'Innodb_buffer_pool_reads',
+    'Innodb_row_lock_time_avg',
+    'Innodb_row_lock_current_waits',
     'questions',
     'slow_queries',
     'threads_created',