Add getter for hasTerminal, terminalColumns and terminalLines on stdout.

tests/standalone/io/stdout_test.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.
+
+import "dart:io";
+
+import "package:expect/expect.dart";
+
+void testTerminalSize() {
+  if (stdout.hasTerminal) {
+    Expect.notEquals(0, stdout.terminalColumns);
+    Expect.notEquals(0, stdout.terminalLines);
+  } else {
+    Expect.throws(() => stdout.terminalColumns, (e) => e is StdoutException);
+    Expect.throws(() => stdout.terminalLines, (e) => e is StdoutException);
+  }
+}
+
+
+void main() {
+  testTerminalSize();
+}