Revert 20969: Reduce usage of IterableMixinWorkaround

sdk/lib/collection/hash_set.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.
 
 part of dart.collection;
 
-/** Common parts of [HashSet] and [LinkedHashSet] implementations. */
-abstract class _HashSetBase<E> extends Collection<E> implements Set<E> {
-  // Set.
-  bool isSubsetOf(Collection<E> other) {
-    // Deprecated, and using old signature.
-    Set otherSet;
-    if (other is Set) {
-      otherSet = other;
-    } else {
-      otherSet = other.toSet();
-    }
-    return otherSet.containsAll(this);
-  }
-
-  bool containsAll(Iterable<E> other) {
-    for (E object in other) {
-      if (!this.contains(object)) return false;
-    }
-    return true;
-  }
-
-  Set<E> intersection(Set<E> other) {
-    Set<E> result = _newSet();
-    if (other.length < this.length) {
-      for (E element in other) {
-        if (this.contains(element)) result.add(element);
-      }
-    } else {
-      for (E element in this) {
-        if (other.contains(element)) result.add(element);
-      }
-    }
-    return result;
-  }
-
-  Set<E> union(Set<E> other) {
-    return _newSet()..addAll(this)..addAll(other);
-  }
-
-  Set<E> difference(Set<E> other) {
-    HashSet<E> result = _newSet();
-    for (E element in this) {
-      if (!other.contains(element)) result.add(element);
-    }
-    return result;
-  }
-
-  String toString() => Collections.collectionToString(this);
-}
-
-class HashSet<E> extends _HashSetBase<E> {
+class HashSet<E> extends Collection<E> implements Set<E> {
   external HashSet();
 
   factory HashSet.from(Iterable<E> iterable) {
     return new HashSet<E>()..addAll(iterable);
   }
 
   // Iterable.
   external Iterator<E> get iterator;
 
   external int get length;
 
   external bool get isEmpty;
 
   external bool contains(Object object);
 
   // Collection.
   external void add(E element);
 
   external void addAll(Iterable<E> objects);
 
   external bool remove(Object object);
 
   external void removeAll(Iterable objectsToRemove);
 
   void retainAll(Iterable objectsToRetain) {
-    Set retainSet;
-    if (objectsToRetain is Set) {
-      retainSet = objectsToRetain;
-    } else {
-      retainSet = objectsToRetain.toSet();
-    }
-    retainWhere(retainSet.contains);
+    IterableMixinWorkaround.retainAll(this, objectsToRetain);
   }
 
   external void removeWhere(bool test(E element));
 
   external void retainWhere(bool test(E element));
 
   external void clear();
 
   // Set.
-  Set<E> _newSet() => new HashSet<E>();
+  bool isSubsetOf(Collection<E> other) {
+    // Deprecated, and using old signature.
+    Set otherSet;
+    if (other is Set) {
+      otherSet = other;
+    } else {
+      otherSet = other.toSet();
+    }
+    return IterableMixinWorkaround.setContainsAll(otherSet, this);
+  }
+
+  bool containsAll(Iterable<E> other) {
+    return IterableMixinWorkaround.setContainsAll(this, other);
+  }
+
+  Set<E> intersection(Set<E> other) {
+    return IterableMixinWorkaround.setIntersection(
+        this, other, new HashSet<E>());
+  }
+
+  Set<E> union(Set<E> other) {
+    return IterableMixinWorkaround.setUnion(this, other, new HashSet<E>());
+  }
+
+  Set<E> difference(Set<E> other) {
+    return IterableMixinWorkaround.setDifference(this, other, new HashSet<E>());
+  }
+
+  String toString() => Collections.collectionToString(this);
 }