ART: Move RegisterNatives helper

Move the helper closer to the users.

Test: m test-art-host
Change-Id: Id05ce5f60af54d0c5aef0c7d8932706c4602fc94
diff --git a/runtime/native/libcore_util_CharsetUtils.cc b/runtime/native/libcore_util_CharsetUtils.cc
index c388ea1..38634e6 100644
--- a/runtime/native/libcore_util_CharsetUtils.cc
+++ b/runtime/native/libcore_util_CharsetUtils.cc
@@ -23,6 +23,7 @@
 #include "jni_internal.h"
 #include "mirror/string.h"
 #include "mirror/string-inl.h"
+#include "native_util.h"
 #include "scoped_fast_native_object_access-inl.h"
 #include "ScopedPrimitiveArray.h"
 #include "unicode/utf16.h"