Add some Dart benchmarks running on fletch.

test/benchmark/for.dart

@@ -0,0 +1,13 @@
+main() {
+  var list = [];
+
+  Stopwatch watch = new Stopwatch();
+  watch.start();
+  for (var i = 0; i < 1000000; i++) list.add(i);
+
+  var sum = 0;
+  for (i in list) sum += i;
+
+  print(sum);
+  print("elapsed: ${watch.elapsedMilliseconds / 1000}");
+}