fixes detection of SDK libraries

tool/input_sdk/private/isolate_helper.dart

 // Copyright (c) 2012, 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 _isolate_helper;
+library dart._isolate_helper;
 
 import 'dart:_js_embedded_names' show
     CLASS_ID_EXTRACTOR,
     CLASS_FIELDS_EXTRACTOR,
     CURRENT_SCRIPT,
     GLOBAL_FUNCTIONS,
     INITIALIZE_EMPTY_INSTANCE,
     INSTANCE_FROM_CLASS_ID;
 
 import 'dart:async';
@@ skipping 1427 matching lines @@
   }
 
   bool operator==(Object other) {
     if (identical(other, this)) return true;
     if (other is CapabilityImpl) {
       return identical(_id, other._id);
     }
     return false;
   }
 }