Use ConstExp for storing constants.

tests/compiler/dart2js/mock_libraries.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.
 
 // Library for creating mock versions of platform and internal libraries.
 
 library mock_libraries;
 
 String buildLibrarySource(
     Map<String, String> elementMap,
@@ skipping 37 matching lines @@
         E get first => null;
         E get last => null;
         E get single => null;
         E removeLast() => null;
         E removeAt(i) => null;
         E elementAt(i) => null;
         E singleWhere(f) => null;
       }''',
   'Map': 'abstract class Map<K,V> {}',
   'Null': 'class Null {}',
-  'num': 'abstract class num {}',
+  'num': r'''
+      abstract class num {
+        operator +(_);
+        operator *(_);
+        operator -();
+      }''',
   'print': 'print(var obj) {}',
   'proxy': 'const proxy = 0;',
   'Object': r'''
       class Object {
         const Object();
         operator ==(other) { return true; }
         get hashCode => throw "Object.hashCode not implemented.";
         String toString() { return null; }
         noSuchMethod(im) { throw im; }
       }''',
   'StackTrace': 'abstract class StackTrace {}',
   'String': 'class String implements Pattern {}',
+  'Symbol': 'class Symbol { final name; const Symbol(this.name); }',
   'Type': 'class Type {}',
   'Pattern': 'abstract class Pattern {}',
 };
 
 const String DEFAULT_PATCH_CORE_SOURCE = r'''
 import 'dart:_js_helper';
 import 'dart:_interceptors';
 import 'dart:_isolate_helper';
 ''';
 
@@ skipping 28 matching lines @@
       r'''checkFunctionSubtype(var target, String signatureName,
                                String contextName, var context,
                                var typeArguments) {}''',
   'checkMalformedType': 'checkMalformedType(value, message) {}',
   'Closure': 'abstract class Closure implements Function { }',
   'closureFromTearOff':
       r'''closureFromTearOff(receiver, functions, reflectionInfo,
                              isStatic, jsArguments, name) {}''',
   'computeSignature':
       'computeSignature(var signature, var context, var contextName) {}',
-  'ConstantMap': 'class ConstantMap {}',
-  'ConstantProtoMap': 'class ConstantProtoMap {}',
-  'ConstantStringMap': 'class ConstantStringMap {}',
+  'ConstantMap': 'class ConstantMap<K, V> {}',
+  'ConstantProtoMap': 'class ConstantProtoMap<K, V> {}',
+  'ConstantStringMap': 'class ConstantStringMap<K, V> {}',
   'copyTypeArguments': 'copyTypeArguments(source, target) {}',
   'createInvocationMirror': 'createInvocationMirror(a0, a1, a2, a3, a4, a5) {}',
   'createRuntimeType': 'createRuntimeType(a) {}',
   'doubleTypeCast': 'doubleTypeCast(value) {}',
   'doubleTypeCheck': 'doubleTypeCheck(value) {}',
   'functionSubtypeCast':
       r'''functionSubtypeCast(Object object, String signatureName,
                               String contextName, var context) {}''',
   'functionTypeTestMetaHelper': r'''
       functionTypeTestMetaHelper() {
@@ skipping 210 matching lines @@
   '_callInIsolate': 'var _callInIsolate;',
   '_WorkerBase': 'class _WorkerBase {}',
 };
 
 const Map<String, String> DEFAULT_MIRRORS_LIBRARY = const <String, String>{
   'Comment': 'class Comment {}',
   'MirrorSystem': 'class MirrorSystem {}',
   'MirrorsUsed': 'class MirrorsUsed {}',
 };