Revert 20969: Reduce usage of IterableMixinWorkaround

sdk/lib/collection/hash_set.dart

Index: sdk/lib/collection/hash_set.dart
diff --git a/sdk/lib/collection/hash_set.dart b/sdk/lib/collection/hash_set.dart
index 04516fc02d7a759ebd3fca97ca8092b70c02cde2..977dcfff5bec0b6a5f12ae072933053af03be6c6 100644
--- a/sdk/lib/collection/hash_set.dart
+++ b/sdk/lib/collection/hash_set.dart
@@ -4,57 +4,7 @@
 
 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) {
@@ -80,13 +30,7 @@ class HashSet<E> extends _HashSetBase<E> {
   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));
@@ -96,5 +40,33 @@ class HashSet<E> extends _HashSetBase<E> {
   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);
 }