dart2js: Change how super tear-offs are registered.

pkg/compiler/lib/src/js_backend/backend_helpers.dart

 // Copyright (c) 2015, 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.js_backend.helpers;
 
 import '../common.dart';
 import '../common/names.dart' show
     Uris;
 import '../common/resolution.dart' show
@@ skipping 369 matching lines @@
   }
 
   Element get consoleTraceHelper {
     return findHelper('consoleTraceHelper');
   }
 
   Element get postTraceHelper {
     return findHelper('postTraceHelper');
   }
 
-  Element get closureFromTearOff {
+  FunctionElement get closureFromTearOff {
     return findHelper('closureFromTearOff');
   }
 
   Element get isJsIndexable {
     return findHelper('isJsIndexable');
   }
 
 
   Element get throwIllegalArgumentException {
     return findHelper('iae');
@@ skipping 272 matching lines @@
   }
 
   Element get findIndexForNativeSubclassType {
     return findInterceptor('findIndexForNativeSubclassType');
   }
 
   Element get convertRtiToRuntimeType {
     return findHelper('convertRtiToRuntimeType');
   }
 }