ART: More header cleanups

Pull out more dependencies through forward declarations.

Test: m test-art-host
Change-Id: I7d86726928937f788b956ec9eac91532d66d57ae
diff --git a/runtime/intern_table.h b/runtime/intern_table.h
index 68454fb..2ec03be 100644
--- a/runtime/intern_table.h
+++ b/runtime/intern_table.h
@@ -25,10 +25,11 @@
 #include "base/mutex.h"
 #include "gc_root.h"
 #include "gc/weak_root_state.h"
-#include "object_callbacks.h"
 
 namespace art {
 
+class IsMarkedVisitor;
+
 namespace gc {
 namespace space {
 class ImageSpace;