feat(core): improve stringify for dart to handle closures

modules/angular2/src/facade/lang.dart

@@ -30,7 +30,15 @@ bool isPromise(obj) => obj is Future;
 bool isNumber(obj) => obj is num;
 bool isDate(obj) => obj is DateTime;
 
-String stringify(obj) => obj.toString();
+String stringify(obj) {
+  final exp = new RegExp(r"from Function '(\w+)'");
+  final str = obj.toString();
+  if (exp.firstMatch(str) != null) {
+    return exp.firstMatch(str).group(1);
+  } else {
+    return str;
+  }
+}
 
 int serializeEnum(val) {
   return val.index;