ART: Move RegisterNatives helper

Move the helper closer to the users.

Test: m test-art-host
Change-Id: Id05ce5f60af54d0c5aef0c7d8932706c4602fc94
diff --git a/runtime/native/java_lang_reflect_Field.cc b/runtime/native/java_lang_reflect_Field.cc
index e38bcd6..f19004d 100644
--- a/runtime/native/java_lang_reflect_Field.cc
+++ b/runtime/native/java_lang_reflect_Field.cc
@@ -28,6 +28,7 @@
 #include "jni_internal.h"
 #include "mirror/class-inl.h"
 #include "mirror/field.h"
+#include "native_util.h"
 #include "reflection-inl.h"
 #include "scoped_fast_native_object_access-inl.h"
 #include "utils.h"