Use ConstExp for storing constants.

sdk/lib/_internal/compiler/implementation/cps_ir/constant_propagation.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.optimizers;
 
 /**
  * Propagates constants throughout the IR, and replaces branches with fixed
  * jumps as well as side-effect free expressions with known constant results.
  * Should be followed by the [ShrinkingReducer] pass.
@@ skipping 61 matching lines @@
     if (cell == null || !cell.isConstant) {
       return null;
     }
 
     assert(continuation.parameters.length == 1);
 
     // Set up the replacement structure.
 
     dart2js.PrimitiveConstant primitiveConstant = cell.constant;
     ConstExp constExp = new PrimitiveConstExp(primitiveConstant);
-    Constant constant = new Constant(constExp, primitiveConstant);
+    Constant constant = new Constant(constExp);
     LetPrim letPrim = new LetPrim(constant);
     InvokeContinuation invoke =
         new InvokeContinuation(continuation, <Definition>[constant]);
 
     invoke.parent = constant.parent = letPrim;
     letPrim.body = invoke;
 
     // Replace the method invocation.
 
     InteriorNode parent = node.parent;
@@ skipping 563 matching lines @@
       return that;
     }
 
     if (this.constant == that.constant) {
       return this;
     }
 
     return NonConst;
   }
 }