Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, 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.
 
 // IrNodes are kept in a separate library to have precise control over their
 // dependencies on other parts of the system.
 library dart2js.ir_nodes;
 
 import '../dart2jslib.dart' as dart2js show Constant, ConstructedConstant,
   StringConstant, ListConstant, MapConstant, invariant;
@@ skipping 432 matching lines @@
 
   Branch(this.condition, Continuation trueCont, Continuation falseCont)
       : trueContinuation = new Reference(trueCont),
         falseContinuation = new Reference(falseCont);
 
   accept(Visitor visitor) => visitor.visitBranch(this);
 }
 
 class Constant extends Primitive {
   final ConstExp expression;
-  final dart2js.Constant value;
 
-  Constant(this.expression, this.value);
+  Constant(this.expression);
+
+  dart2js.Constant get value => expression.value;
 
   accept(Visitor visitor) => visitor.visitConstant(this);
 }
 
 class This extends Primitive {
   This();
 
   accept(Visitor visitor) => visitor.visitThis(this);
 }
 
@@ skipping 469 matching lines @@
       release(node.parameters[i]);
     }
   }
 
   void visitIsTrue(IsTrue node) {
     visitReference(node.value);
   }
 
 }