Use ConstExp for storing constants.

tests/compiler/dart2js/backend_dart/sexpr_test.dart

 // Copyright (c) 2014, 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.
 
 import '../compiler_helper.dart';
 import 'sexpr_unstringifier.dart';
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 import 'package:compiler/implementation/dart2jslib.dart';
@@ skipping 119 matching lines @@
         }
 
         return sexprs;
       });
 }
 
 /// Checks if the generated S-expressions can be processed by the unstringifier,
 /// returns the resulting definitions.
 List<FunctionDefinition> testUnstringifier(List<String> sexprs) {
   return sexprs.map((String sexpr) {
-    final function = new SExpressionUnstringifier().unstringify(sexpr);
-    Expect.isNotNull(function, "Unstringification failed:\n\n$sexpr");
-    return function;
+    try {
+      final function = new SExpressionUnstringifier().unstringify(sexpr);
+      Expect.isNotNull(function, "Unstringification failed:\n\n$sexpr");
+      return function;
+    } catch (e, s) {

[karlklose, 2014/09/25 08:43:25]

Why this change? Is this debug code or is the stacktrace not showing correclty
in the test setup>

[Johnni Winther, 2014/09/29 08:24:44]

On error the unstringifier now throws instead of asserting. This improves the
messaging in case of failures.

+      print('$e\n$s');
+      Expect.fail('Error unstringifying "$sexpr": $e');
+    }
   }).toList();
 }
 
 void main() {
   final tokens =
           [ "FunctionDefinition"
           , "IsTrue"
 
           // Expressions
           , "Branch"
@@ skipping 21 matching lines @@
           ];
 
   asyncTest(() => testStringifier(CODE, tokens).then((List<String> sexprs) {
     final functions = testUnstringifier(sexprs);
 
     // Ensure that
     // stringified(CODE) == stringified(unstringified(stringified(CODE)))
     Expect.listEquals(sexprs, stringifyAll(functions));
   }));
 }