Fix sdk/lib/io errors found by the analyzer.

sdk/lib/io/stdio.dart

Index: sdk/lib/io/stdio.dart
diff --git a/sdk/lib/io/stdio.dart b/sdk/lib/io/stdio.dart
index 073903dbfe2d3e8aab0d2961a7a62bfce5a3e759..76abe057fe060eb987d6884b03a710f900d2fd81 100644
--- a/sdk/lib/io/stdio.dart
+++ b/sdk/lib/io/stdio.dart
@@ -162,7 +162,8 @@ class _StdSink implements IOSink {
   void writeln([object = "" ]) => _sink.writeln(object);
   void writeAll(objects, [sep = ""]) => _sink.writeAll(objects, sep);
   void add(List<int> data) => _sink.add(data);
-  void addError(error) => _sink.addError(error);
+  void addError(error, [StackTrace stackTrace]) =>
+      _sink.addError(error, stackTrace);
   void writeCharCode(int charCode) => _sink.writeCharCode(charCode);
   Future addStream(Stream<List<int>> stream) => _sink.addStream(stream);
   Future close() => _sink.close();