Add Process.runSync for running processe synchronously.

tests/standalone/io/process_sync_script.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.
+//
+// Utility script to generate some output on stdout and stderr.
+
+import "dart:math";
+import "dart:io";
+
+main() {
+  var options = new Options();
+  var blockCount = int.parse(options.arguments[0]);
+  var stdoutBlockSize = int.parse(options.arguments[1]);
+  var stderrBlockSize = int.parse(options.arguments[2]);
+  var stdoutBlock =
+      new String.fromCharCodes(new List.filled(stdoutBlockSize, 65));
+  var stderrBlock =
+      new String.fromCharCodes(new List.filled(stderrBlockSize, 66));
+  for (int i = 0; i < blockCount; i++) {
+    stdout.write(stdoutBlock);
+    stderr.write(stderrBlock);
+  }
+  exit(int.parse(options.arguments[3]));
+}