Use ConstExp for storing constants.

tests/compiler/dart2js/mock_compiler.dart

 // Copyright (c) 2012, 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.
 
 library mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:collection';
 
@@ skipping 345 matching lines @@
 
 // The mock compiler does not split the program in output units.
 class MockDeferredLoadTask extends DeferredLoadTask {
   MockDeferredLoadTask(Compiler compiler) : super(compiler);
 
   OutputUnit getElementOutputUnit(dynamic dependency) {
     return mainOutputUnit;
   }
 }
 
-api.DiagnosticHandler createHandler(MockCompiler compiler, String text) {
+api.DiagnosticHandler createHandler(MockCompiler compiler, String text,
+                                    {bool verbose: false}) {
   return (uri, int begin, int end, String message, kind) {
+    if (kind == api.Diagnostic.VERBOSE_INFO && !verbose) return;
     SourceFile sourceFile;
     if (uri == null) {
       sourceFile = new StringSourceFile('analysis', text);
     } else {
       sourceFile = compiler.sourceFiles[uri.toString()];
     }
     if (sourceFile != null && begin != null && end != null) {
       print(sourceFile.getLocationMessage(message, begin, end, true, (x) => x));
     } else {
       print(message);
     }
   };
 }
 
 class MockElement extends FunctionElementX {
   MockElement(Element enclosingElement)
       : super('', ElementKind.FUNCTION, Modifiers.EMPTY,
               enclosingElement, false);
 
   get node => null;
 
   parseNode(_) => null;
 
   bool get hasNode => false;
 }