"Reverting 19985"

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 ca32220cf7dcf6aafabd289480b6f829ef174e03..48331100aec62487e2ea622035b6468328ceaeac 100644
--- a/sdk/lib/collection/hash_set.dart
+++ b/sdk/lib/collection/hash_set.dart
@@ -86,19 +86,12 @@ class HashSet<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 IterableMixinWorkaround.setContainsAll(otherSet, this);
+  bool isSubsetOf(Set<E> other) {
+    return IterableMixinWorkaround.isSubsetOfSet(this, other);
   }
 
-  bool containsAll(Iterable<E> other) {
-    return IterableMixinWorkaround.setContainsAll(this, other);
+  bool containsAll(Set<E> other) {
+    return IterableMixinWorkaround.isSubsetOfSet(other, this);
   }
 
   Set<E> intersection(Set<E> other) {