SDK fixes

test/dart_codegen/expect/collection/set.dart

 part of dart.collection;
  abstract class SetMixin<E> implements Set<E> {bool add(E element);
  bool contains(Object element);
- E lookup(E element);
+ E lookup(Object element);
  bool remove(Object element);
  Iterator<E> get iterator;
  Set<E> toSet();
  int get length;
  bool get isEmpty => length == 0;
  bool get isNotEmpty => length != 0;
  void clear() {
   removeAll(toList());
   }
  void addAll(Iterable<E> elements) {
@@ skipping 189 matching lines @@
    int elementIndex = 0;
    for (E element in this) {
     if (index == elementIndex) return element;
      elementIndex++;
     }
    throw new RangeError.index(index, this, "index", null, elementIndex);
   }
 }
  abstract class SetBase<E> extends SetMixin<E> {static String setToString(Set set) => IterableBase.iterableToFullString(set, '{', '}');
 }