dart2js cps: Keep interceptors in a separate field.

pkg/compiler/lib/src/js_backend/codegen/glue.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 code_generator_dependencies;
 
 import '../backend_helpers.dart' show
     BackendHelpers;
 import '../js_backend.dart';
 
@@ skipping 281 matching lines @@
 
   FunctionElement get closureFromTearOff => _backend.helpers.closureFromTearOff;
 
   js.Name registerOneShotInterceptor(Selector selector) {
     return _backend.registerOneShotInterceptor(selector);
   }
 
   bool mayGenerateInstanceofCheck(DartType type) {
     return _backend.mayGenerateInstanceofCheck(type);
   }
+
+  bool methodUsesReceiverArgument(FunctionElement function) {
+    assert(isInterceptedMethod(function));
+    ClassElement class_ = function.enclosingClass.declaration;
+    return isInterceptorClass(class_) || isUsedAsMixin(class_);
+  }
 }