Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/elements/elements.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 elements;
 
 
+import '../cps_ir/const_expression.dart';
 import '../tree/tree.dart';
 import '../util/util.dart';
 import '../resolution/resolution.dart';
 
 import '../dart2jslib.dart' show InterfaceType,
                                  DartType,
                                  TypeVariableType,
                                  TypedefType,
                                  DualKind,
                                  MessageKind,
@@ skipping 1402 matching lines @@
   /// The [type] defined by the type variable.
   TypeVariableType get type;
 
   /// The upper bound on the type variable. If not explicitly declared, this is
   /// `Object`.
   DartType get bound;
 }
 
 abstract class MetadataAnnotation implements Spannable {
   /// The front-end constant of this metadata annotation.
-  Constant get value;
+  ConstExp get constant;
   Element get annotatedElement;
   int get resolutionState;
   Token get beginToken;
   Token get endToken;
 
   MetadataAnnotation ensureResolved(Compiler compiler);
 }
 
 /// An [Element] that has a type.
 abstract class TypedElement extends Element {
@@ skipping 117 matching lines @@
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }