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

sdk/lib/io/stdio.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 const int _STDIO_HANDLE_TYPE_TERMINAL = 0;
 const int _STDIO_HANDLE_TYPE_PIPE = 1;
 const int _STDIO_HANDLE_TYPE_FILE = 2;
 const int _STDIO_HANDLE_TYPE_SOCKET = 3;
@@ skipping 144 matching lines @@
   _StdSink(IOSink this._sink);
 
   Encoding get encoding => _sink.encoding;
   void set encoding(Encoding encoding) {
     _sink.encoding = encoding;
   }
   void write(object) => _sink.write(object);
   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();
   Future get done => _sink.done;
 }
 
 class StdioType {
   static const StdioType TERMINAL = const StdioType._("terminal");
   static const StdioType PIPE = const StdioType._("pipe");
   static const StdioType FILE = const StdioType._("file");
@@ skipping 60 matching lines @@
   }
   return StdioType.OTHER;
 }
 
 
 class _StdIOUtils {
   external static IOSink _getStdioOutputStream(int fd);
   external static Stdin _getStdioInputStream();
   external static int _socketType(nativeSocket);
 }