Update dart2js unit tests to new library API.

dart/tests/compiler/dart2js/for_in_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 'compiler_helper.dart';
+
+const String TEST_ONE = r"""
+foo(a) {
+  int x = 0;
+  for (int i in a) {
+    x += i;
+  }
+  return x;
+}
+""";
+
+const String TEST_TWO = r"""
+foo(a) {
+  int x = 0;
+  for (int i in a) {
+    if (i == 5) continue;
+    x += i;
+  }
+  return x;
+}
+""";
+
+main() {
+  String generated = compile(TEST_ONE, entry: 'foo');
+  Expect.isTrue(!generated.contains(r'break'));
+  generated = compile(TEST_TWO, entry: 'foo');
+  Expect.isTrue(generated.contains(r'continue'));
+}