Add structural equality to ConstantExpression.

pkg/compiler/lib/src/tree_ir/tree_ir_nodes.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 tree_ir_nodes;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, GenericType, InterfaceType, TypeVariableType;
 import '../elements/elements.dart';
@@ skipping 255 matching lines @@
 }
 
 /**
  * A constant.
  */
 class Constant extends Expression {
   final ConstantExpression expression;
 
   Constant(this.expression);
 
-  Constant.primitive(values.PrimitiveConstantValue primitiveValue)
-      : expression = new PrimitiveConstantExpression(primitiveValue);
+  Constant.bool(values.BoolConstantValue constantValue)
+      : expression = new BoolConstantExpression(
+          constantValue.primitiveValue, constantValue);
 
   accept(ExpressionVisitor visitor) => visitor.visitConstant(this);
   accept1(ExpressionVisitor1 visitor, arg) => visitor.visitConstant(this, arg);
 
   values.ConstantValue get value => expression.value;
 }
 
 class This extends Expression {
   accept(ExpressionVisitor visitor) => visitor.visitThis(this);
   accept1(ExpressionVisitor1 visitor, arg) => visitor.visitThis(this, arg);
@@ skipping 1100 matching lines @@
   visitReadTypeVariable(ReadTypeVariable node) {
     node.target = visitExpression(node.target);
     return node;
   }
 
   visitTypeExpression(TypeExpression node) {
     _replaceExpressions(node.arguments);
     return node;
   }
 }