dart2js cps: Support function types in 'is' and 'as' operators.

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 2039 matching lines @@
 
   /// 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);
   }
 
   FunctionElement get throwTypeErrorHelper => _backend.getThrowTypeError();
 
   ClassElement get nullClass => _compiler.nullClass;
+
+  DartType unaliasType(DartType type) => type.unalias(_compiler);
 }
 
 /// 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.
@@ skipping 790 matching lines @@
   }
 
   processSetStatic(ir.SetStatic node) {
     node.body = replacementFor(node.body);
   }
 
   processContinuation(ir.Continuation node) {
     node.body = replacementFor(node.body);
   }
 }