Fix expectation for 53-bit-overflow.

runtime/lib/errors_patch.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.
 
 patch class Error {
   /* patch */ static String _objectToString(Object object) {
     return Object._toString(object);
   }
 }
 
@@ skipping 153 matching lines @@
           "method named '$_memberName'\n"
           "Receiver: $receiver_str\n"
           "Tried calling: $_memberName($actualParameters)\n"
           "Found: $_memberName($formalParameters)");
     }
     return msg_buf.toString();
   }
 }
 
 class _FiftyThreeBitOverflowError implements Error {
-  final Object value;
+  final Object _value;
 
-  const _FiftyThreeBitOverflowError(this.value);
-  String toString() => "53-bit Overflow: $value";
+  const _FiftyThreeBitOverflowError(this._value);
+  String toString() => "53-bit Overflow: $_value";
 }