Add corelib tests

test/codegen/corelib/iterable_first_test.dart

+// Copyright (c) 2012, 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 "package:expect/expect.dart";
+
+main() {
+  List<int> list1 = <int>[1, 2, 3];
+  List<int> list2 = const <int>[4, 5];
+  List<String> list3 = <String>[];
+  Set<int> set1 = new Set<int>();
+  set1..add(11)
+      ..add(12)
+      ..add(13);
+  Set set2 = new Set();
+
+  Expect.equals(1, list1.first);
+  Expect.equals(4, list2.first);
+  Expect.throws(() => list3.first, (e) => e is StateError);
+
+  Expect.isTrue(set1.contains(set1.first));
+
+  Expect.throws(() => set2.first, (e) => e is StateError);
+}