Handle for-in loops

test/dart_codegen/expect/collection/splay_tree.dart

 part of dart.collection;
  typedef bool _Predicate<T>(T value);
  class _SplayTreeNode<K> {final K key;
  _SplayTreeNode<K> left;
  _SplayTreeNode<K> right;
  _SplayTreeNode(K this.key);
 }
  class _SplayTreeMapNode<K, V> extends _SplayTreeNode<K> {V value;
  _SplayTreeMapNode(K key, V this.value) : super(key);
 }
@@ skipping 415 matching lines @@
 }
 ), DEVC$RT.type((_SplayTreeNode<K> _) {
 }
 ), "CompositeCast", """line 644, column 55 of dart:collection/splay_tree.dart: """, node is _SplayTreeNode<K>, false);
 }
  class SplayTreeSet<E> extends _SplayTree<E> with IterableMixin<E>, SetMixin<E> {Comparator _comparator;
  _Predicate _validKey;
  SplayTreeSet([int compare(E key1, E key2), bool isValidKey(potentialKey)]) : _comparator = ((__x36) => DEVC$RT.cast(__x36, dynamic, __t33, "CompositeCast", """line 693, column 23 of dart:collection/splay_tree.dart: """, __x36 is __t33, false))((compare == null) ? Comparable.compare : compare), _validKey = ((__x37) => DEVC$RT.cast(__x37, dynamic, __t24, "CompositeCast", """line 694, column 21 of dart:collection/splay_tree.dart: """, __x37 is __t24, false))((isValidKey != null) ? isValidKey : ((v) => v is E));
  factory SplayTreeSet.from(Iterable elements, [int compare(E key1, E key2), bool isValidKey(potentialKey)]) {
 SplayTreeSet<E> result = new SplayTreeSet<E>(compare, isValidKey);
- for (final E element in elements) {
+ for (final E element in DEVC$RT.cast(elements, DEVC$RT.type((Iterable<dynamic> _) {
+}
+), DEVC$RT.type((Iterable<E> _) {
+}
+), "CompositeCast", """line 707, column 29 of dart:collection/splay_tree.dart: """, elements is Iterable<E>, false)) {
 result.add(element);
 }
  return result;
 }
  int _compare(E e1, E e2) => _comparator(e1, e2);
  Iterator<E> get iterator => new _SplayTreeKeyIterator<E>(this);
  int get length => _count;
  bool get isEmpty => _root == null;
  bool get isNotEmpty => _root != null;
  E get first {
@@ skipping 119 matching lines @@
 _clear();
 }
  Set<E> toSet() => _clone();
  String toString() => IterableBase.iterableToFullString(this, '{', '}');
 }
  typedef int __t20<K>(K __u21, K __u22);
  typedef bool __t24(dynamic __u25);
  typedef int __t30<K>(K __u31, K __u32);
  typedef int __t33(dynamic __u34, dynamic __u35);
  typedef int __t42<E>(E __u43, E __u44);