Add SetBase/SetMixin.

runtime/lib/collection_patch.dart

Index: runtime/lib/collection_patch.dart
diff --git a/runtime/lib/collection_patch.dart b/runtime/lib/collection_patch.dart
index 81aa289f17ebc60e01e8982f2ca2cd7949a5843d..e72c086fc55a12438ac26c12ba0d82afa44823c1 100644
--- a/runtime/lib/collection_patch.dart
+++ b/runtime/lib/collection_patch.dart
@@ -540,7 +540,7 @@ patch class HashSet<E> {
   /* patch */ factory HashSet.identity() = _IdentityHashSet<E>;
 }
 
-class _HashSet<E> extends _HashSetBase<E> implements HashSet<E> {
+class _HashSet<E> extends SetBase<E> implements HashSet<E> {
   static const int _INITIAL_CAPACITY = 8;
 
   List<_HashSetEntry> _buckets = new List(_INITIAL_CAPACITY);
@@ -634,10 +634,6 @@ class _HashSet<E> extends _HashSetBase<E> implements HashSet<E> {
     }
   }
 
-  void retainAll(Iterable<Object> objectsToRetain) {
-    super._retainAll(objectsToRetain, (o) => o is E);
-  }
-
   void _filterWhere(bool test(E element), bool removeMatching) {
     int length = _buckets.length;
     for (int index =  0; index < length; index++) {
@@ -711,13 +707,13 @@ class _HashSet<E> extends _HashSetBase<E> implements HashSet<E> {
     _buckets = newBuckets;
   }
 
-  HashSet<E> _newSet() => new _HashSet<E>();
+  HashSet<E> cloneEmpty() => new _HashSet<E>();
 }
 
 class _IdentityHashSet<E> extends _HashSet<E> {
   int _hashCode(e) => identityHashCode(e);
   bool _equals(e1, e2) => identical(e1, e2);
-  HashSet<E> _newSet() => new _IdentityHashSet<E>();
+  HashSet<E> cloneEmpty() => new _IdentityHashSet<E>();
 }
 
 class _CustomHashSet<E> extends _HashSet<E> {
@@ -757,14 +753,11 @@ class _CustomHashSet<E> extends _HashSet<E> {
     }
   }
 
-  void retainAll(Iterable<Object> elements) {
-    super._retainAll(elements, _validKey);
-  }
-
   bool _equals(e1, e2) => _equality(e1, e2);
   int _hashCode(e) => _hasher(e);
 
-  HashSet<E> _newSet() => new _CustomHashSet<E>(_equality, _hasher, _validKey);
+  HashSet<E> cloneEmpty() =>
+      new _CustomHashSet<E>(_equality, _hasher, _validKey);
 }
 
 class _HashSetEntry {
@@ -1174,13 +1167,13 @@ class _LinkedHashSet<E> extends _HashSet<E>
     super.clear();
   }
 
-  HashSet<E> _newSet() => new _LinkedHashSet<E>();
+  HashSet<E> cloneEmpty() => new _LinkedHashSet<E>();
 }
 
 class _LinkedIdentityHashSet<E> extends _LinkedHashSet<E> {
   int _hashCode(e) => identityHashCode(e);
   bool _equals(e1, e2) => identical(e1, e2);
-  HashSet<E> _newSet() => new _LinkedIdentityHashSet<E>();
+  HashSet<E> cloneEmpty() => new _LinkedIdentityHashSet<E>();
 }
 
 class _LinkedCustomHashSet<E> extends _LinkedHashSet<E> {
@@ -1225,11 +1218,7 @@ class _LinkedCustomHashSet<E> extends _LinkedHashSet<E> {
     }
   }
 
-  void retainAll(Iterable<Object> elements) {
-    super._retainAll(elements, _validKey);
-  }
-
-  HashSet<E> _newSet() =>
+  HashSet<E> cloneEmpty() =>
       new _LinkedCustomHashSet<E>(_equality, _hasher, _validKey);
 }