Implement the invoke methods (invoke, getField, setField, newInstance, apply) as internal natives.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 25019)
+++ runtime/vm/object.cc	(working copy)
@@ -2738,6 +2738,10 @@
   ReusableHandleScope reused_handles(isolate);
   Array& flds = reused_handles.ArrayHandle();
   flds ^= fields();
+  if (flds.IsNull()) {
+    // This can occur, e.g., for Null classes.
+    return Field::null();
+  }
   Field& field = reused_handles.FieldHandle();
   String& field_name = reused_handles.StringHandle();
   intptr_t len = flds.Length();