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

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.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.
 
 library dart2js.ir_builder_task;
 
 import '../closure.dart' as closurelib;
 import '../closure.dart' hide ClosureScope;
 import '../constants/expressions.dart';
 import '../dart_types.dart';
@@ skipping 2288 matching lines @@
   final Compiler _compiler;
   JavaScriptBackend get _backend => _compiler.backend;
 
   GlobalProgramInformation(this._compiler);
 
   /// Returns [true], if the analysis could not determine that the type
   /// arguments for the class [cls] are never used in the program.
   bool requiresRuntimeTypesFor(ClassElement cls) {
     return cls.typeVariables.isNotEmpty && _backend.classNeedsRti(cls);
   }
+
+  Set<ClassElement> get interceptedClasses => _backend.interceptedClasses;
 }
 
 /// IR builder specific to the JavaScript backend, coupled to the [JsIrBuilder].
 class JsIrBuilderVisitor extends IrBuilderVisitor {
   /// Promote the type of [irBuilder] to [JsIrBuilder].
   JsIrBuilder get irBuilder => super.irBuilder;
 
   JavaScriptBackend get backend => compiler.backend;
 
   /// Result of closure conversion for the current body of code.
   ///
   /// Will be initialized upon entering the body of a function.
   /// It is computed by the [ClosureTranslator].
   ClosureClassMap closureClassMap;
 
   /// During construction of a constructor factory, [fieldValues] maps fields
   /// to the primitive containing their initial value.
   Map<FieldElement, ir.Primitive> fieldValues = <FieldElement, ir.Primitive>{};
 
   JsIrBuilderVisitor(TreeElements elements,
                      Compiler compiler,
                      SourceInformationBuilder sourceInformationBuilder)
       : super(elements, compiler, sourceInformationBuilder);
 
+
   /// Builds the IR for creating an instance of the closure class corresponding
   /// to the given nested function.
   ClosureClassElement makeSubFunction(ast.FunctionExpression node) {
     ClosureClassMap innerMap =
         compiler.closureToClassMapper.getMappingForNestedFunction(node);
     ClosureClassElement closureClass = innerMap.closureClassElement;
     return closureClass;
   }
 
   ir.Primitive visitFunctionExpression(ast.FunctionExpression node) {
@@ skipping 733 matching lines @@
     node.body = replacementFor(node.body);
   }
 }
 
 /// Visit a just-deleted subterm and unlink all [Reference]s in it.
 class RemovalVisitor extends ir.RecursiveVisitor {
   processReference(ir.Reference reference) {
     reference.unlink();
   }
 }