Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/helpers/stats.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.
 
 part of dart2js.helpers;
 
 // Helper methods for statistics.
 
 /// Current stats collector. Use [enableStatsOutput] to enable recording of
 /// stats.
 Stats get stats {
+  enableDebugMode();
   if (_stats == null) {
     _stats = const Stats();
   }
   return _stats;
 }
 
 Stats _stats;
 
 /// Enable recording of stats. Use [Stats.dumpStats] to output the record stats.
 ///
 /// Pass the [outputProvider] of [Compiler] to generate stats into a separate
 /// file using [name] and [extension] for the filename. If omitted, stats are
 /// printed on standard out.
 ///
 /// If [xml] is `true`, stats output is formatted as XML with a default
 /// extension of 'xml', otherwise the output is indented text with a default
 /// extension of 'log'.
 void enableStatsOutput({CompilerOutputProvider outputProvider,
                         bool xml: true,
                         String name: 'stats',
                         String extension,
                         int examples: 10}) {
   if (_stats != null) {
     throw new StateError('Stats have already been initialized.');
   }
+  enableDebugMode();
+
   StatsOutput output;
   if (outputProvider != null) {
     if (extension == null) {
       extension = xml ? 'xml' : 'log';
     }
     output = new SinkOutput(outputProvider(name, extension));
   } else {
     output = const DebugOutput();
   }
   StatsPrinter printer;
@@ skipping 729 matching lines @@
 /// Returns a new map in which the keys of [map] are sorted using [compare].
 /// If [compare] is null, the keys must be [Comparable].
 Map sortMap(Map map, [int compare(a,b)]) {
   List keys = map.keys.toList();
   keys.sort(compare);
   Map sortedMap = new Map();
   keys.forEach((k) => sortedMap[k] = map[k]);
   return sortedMap;
 }