Reapply "Make LinkedHashMap also have a factory constructor and be customizable""

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 e161d5a3153c59b32818b1f305e42e2a3a556f4d..d5df0ca45b609c8fbf5e17317df97af1ff81e003 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 LinkedHashMap<String,String> {
+class Crash extends HashSet<String> {
   Crash(): super();
 }
 
 void main() {
   Crash map = new Crash();
-  Expect.isTrue(map is LinkedHashMap);
+  Expect.isTrue(map is HashSet);
 }