Avoid reparsing metadata expressions

tests/compiler/dart2js_extra/23404_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Regression test for http://dartbug.com/23404/
+import 'package:expect/expect.dart';
+
+// Dart2js crashed when the global metadata had escaped characters. That
+// happens, for example, when tearing off a function that uses a default
+// argument containing escape characters.
+foo([a='\u00a0']) => a;
+bar() => '';
+
+@NoInline
+@AssumeDynamic
+confuse(x) => x;
+
+main() {
+  Expect.equals('\u00a0', confuse(foo)());
+  Expect.equals('', confuse(bar)());
+}