Make lock debug checks optional.

Move all locking checks behing kDebugLocking. Disable locking checks
when not DEBUG. Will enable later so that we can get some idea of the
performance overhead. We want locking checks to be the default for a
while to make sure we solve any remaining potential deadlock issues.

Change-Id: I4d7622750cc29f9933c84259796de5a2df02b783
diff --git a/src/atomic.cc b/src/atomic.cc
index b923f91..fb4de9c 100644
--- a/src/atomic.cc
+++ b/src/atomic.cc
@@ -17,6 +17,7 @@
 #include "atomic.h"
 
 #include <pthread.h>
+#include <vector>
 
 #include "mutex.h"
 #include "stl_util.h"