ART: More header cleanups

Pull out more dependencies through forward declarations.

Test: m test-art-host
Change-Id: I7d86726928937f788b956ec9eac91532d66d57ae
diff --git a/runtime/gc/reference_queue.cc b/runtime/gc/reference_queue.cc
index fd5dcf9..321d22a 100644
--- a/runtime/gc/reference_queue.cc
+++ b/runtime/gc/reference_queue.cc
@@ -22,6 +22,7 @@
 #include "mirror/class-inl.h"
 #include "mirror/object-inl.h"
 #include "mirror/reference-inl.h"
+#include "object_callbacks.h"
 
 namespace art {
 namespace gc {