dart2js cps: Always use interceptors and type tags for 'is' checks.

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 312 matching lines @@
   final List<LiteralMapEntry> entries;
 
   LiteralMap(this.type, this.entries);
 
   accept(ExpressionVisitor visitor) => visitor.visitLiteralMap(this);
   accept1(ExpressionVisitor1 visitor, arg) {
     return visitor.visitLiteralMap(this, arg);
   }
 }
 
+/// Given the interceptor for a value, test the value against a type.
 class TypeOperator extends Expression {
   Expression receiver;
   final DartType type;
   final bool isTypeTest;
 
   TypeOperator(this.receiver, this.type, {bool this.isTypeTest});
 
   accept(ExpressionVisitor visitor) => visitor.visitTypeOperator(this);
   accept1(ExpressionVisitor1 visitor, arg) {
     return visitor.visitTypeOperator(this, arg);
@@ skipping 1111 matching lines @@
   visitTypeExpression(TypeExpression node) {
     _replaceExpressions(node.arguments);
     return node;
   }
 
   visitCreateInvocationMirror(CreateInvocationMirror node) {
     _replaceExpressions(node.arguments);
     return node;
   }
 }