Don't use ES6 map if browser has no Map

sdk/lib/_internal/compiler/js_lib/collection_patch.dart

Index: sdk/lib/_internal/compiler/js_lib/collection_patch.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
index 55af330c55d4a1a489eb0bbb2bdf92ecd8808080..74582ba193f18160850f78df8bc075e1837b3ce8 100644
--- a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
+++ b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
@@ -554,8 +554,8 @@ class _LinkedIdentityHashMap<K, V> extends JsLinkedHashMap<K, V> {
 
   factory _LinkedIdentityHashMap.es6() {
     return (_USE_ES6_MAPS && _LinkedIdentityHashMap._supportsEs6Maps)
-        ? new _LinkedIdentityHashMap<K, V>()
-        : new _Es6LinkedIdentityHashMap<K, V>();
+        ? new _Es6LinkedIdentityHashMap<K, V>()
+        : new _LinkedIdentityHashMap<K, V>();
   }
 
   _LinkedIdentityHashMap();