Deprecate Set.isSubsetOf, make Set.containsAll accept iterable.

sdk/lib/collection/collections.dart

Index: sdk/lib/collection/collections.dart
diff --git a/sdk/lib/collection/collections.dart b/sdk/lib/collection/collections.dart
index 4cf7daf326a7993183ad17b377a0f3ce0d5f2f1e..5d8431743f585b374bf0a0a76430ca4d10fb6fdb 100644
--- a/sdk/lib/collection/collections.dart
+++ b/sdk/lib/collection/collections.dart
@@ -382,15 +382,13 @@ class IterableMixinWorkaround {
     return new ListMapView(l);
   }
 
-  static bool isSubsetOfSet(Set set, Set other) {
-    if (set.length > other.length) return false;
-    for (var element in set) {
-      if (!other.contains(element)) return false;
+  static bool setContainsAll(Set set, Iterable other) {
+    for (var element in other) {
+      if (!set.contains(element)) return false;
     }
     return true;
   }
 
-
   static Set setIntersection(Set set, Set other, Set result) {
     Set smaller;
     Set larger;