Fix JDWP ObjectRegistry lock ordering.

Also make debugging lock ordering violations nicer by using our
LockLevel operator<<.

Change-Id: Ic15ebe70363a90a09f6491bd5c336a604e9d6c48
diff --git a/src/thread.h b/src/thread.h
index 7f8bd7e..1992dc9 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -769,7 +769,7 @@
   pthread_t pthread_self_;
 
   // Support for Mutex lock hierarchy bug detection.
-  BaseMutex* held_mutexes_[kMaxMutexLevel + 1];
+  BaseMutex* held_mutexes_[kLockLevelCount];
 
   // A positive value implies we're in a region where thread suspension isn't expected.
   uint32_t no_thread_suspension_;