Use correct output encoding in Process.runSync.

runtime/bin/process_patch.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.
 
 patch class _WindowsCodePageDecoder {
   /* patch */ static String _decodeBytes(List<int> bytes)
       native "SystemEncodingToString";
 }
 
 
@@ skipping 305 matching lines @@
                                  status._errorCode);
     }
 
     var result = _wait(
         _stdin._sink._nativeSocket,
         _stdout._stream._nativeSocket,
         _stderr._stream._nativeSocket,
         _exitHandler._nativeSocket);
 
     getOutput(output, encoding) {
-      if (stderrEncoding == null) return output;
+      if (encoding == null) return output;
       return encoding.decode(output);
     }
 
     return new _ProcessResult(
         result[0],
         result[1],
         getOutput(result[2], stdoutEncoding),
         getOutput(result[3], stderrEncoding));
   }
 
@@ skipping 130 matching lines @@
   const _ProcessResult(int this.pid,
                        int this.exitCode,
                        this.stdout,
                        this.stderr);
 
   final int pid;
   final int exitCode;
   final stdout;
   final stderr;
 }