Experimental version without native constructor support

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 1172)
+++ runtime/vm/parser.cc	(working copy)
@@ -1730,7 +1730,7 @@
   } else if (CurrentToken() == Token::kARROW) {
     ErrorMsg("constructors may not return a value");
   } else if (IsLiteral("native")) {
-    ParseNativeFunctionBlock(&params, func);
+    ErrorMsg("native constructors not supported");
   } else if (CurrentToken() == Token::kSEMICOLON) {
     // Some constructors have no function body.
     ConsumeToken();