ART: Clean up includes.

Reduce dependencies to improve incremental build times.
Break up circular dependency involving class_linker-inl.h.

Change-Id: I4be742c5c2b5cd9855beea86630fd68aab76b0db
diff --git a/runtime/monitor_test.cc b/runtime/monitor_test.cc
index 6d1e721..2351463 100644
--- a/runtime/monitor_test.cc
+++ b/runtime/monitor_test.cc
@@ -20,6 +20,7 @@
 #include <string>
 
 #include "atomic.h"
+#include "class_linker-inl.h"
 #include "common_runtime_test.h"
 #include "handle_scope-inl.h"
 #include "mirror/class-inl.h"