Reapply "Convert HashSet, LinkedHashSet to factory methods and custom implementations."

tests/language/issue9949_test.dart

Index: tests/language/issue9949_test.dart
diff --git a/tests/language/issue9949_test.dart b/tests/language/issue9949_test.dart
index d5df0ca45b609c8fbf5e17317df97af1ff81e003..46c73d21892eb654f9caa3143da3ad552fd311e1 100644
--- a/tests/language/issue9949_test.dart
+++ b/tests/language/issue9949_test.dart
@@ -8,11 +8,11 @@
 import "package:expect/expect.dart";
 import 'dart:collection';
 
-class Crash extends HashSet<String> {
+class Crash extends Expando<String> {
   Crash(): super();
 }
 
 void main() {
-  Crash map = new Crash();
-  Expect.isTrue(map is HashSet);
+  Crash expando = new Crash();
+  Expect.isTrue(expando is Expando);
 }