Revert "Use an ES6 map for a linked identity hash map."

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

Index: sdk/lib/_internal/compiler/js_lib/linked_hash_map.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/linked_hash_map.dart b/sdk/lib/_internal/compiler/js_lib/linked_hash_map.dart
index 5326e1b5debf6e52eeeef5a6b6003780a26b7bee..bbf76d3b6a9432954af7865ea0dfb9f5d2f97a90 100644
--- a/sdk/lib/_internal/compiler/js_lib/linked_hash_map.dart
+++ b/sdk/lib/_internal/compiler/js_lib/linked_hash_map.dart
@@ -44,7 +44,7 @@ class JsLinkedHashMap<K, V> implements LinkedHashMap<K, V>, InternalMap {
   /// If ES6 Maps are available returns a linked hash-map backed by an ES6 Map.
   @ForceInline()
   factory JsLinkedHashMap.es6() {
-    return (_USE_ES6_MAPS && JsLinkedHashMap._supportsEs6Maps)
+    return (_USE_ES6_MAPS  && JsLinkedHashMap._supportsEs6Maps)
         ? new Es6LinkedHashMap<K, V>()
         : new JsLinkedHashMap<K, V>();
   }