Support creating elements from IR nodes in JsKernelToElementMap

tests/compiler/dart2js/js_model/model_test.dart

Index: tests/compiler/dart2js/js_model/model_test.dart
diff --git a/tests/compiler/dart2js/js_model/model_test.dart b/tests/compiler/dart2js/js_model/model_test.dart
index f9a64b27592ef2a57b31e1be8003fd23e3b4910e..f17347f3363c710596101c53390c9019bc1e89ea 100644
--- a/tests/compiler/dart2js/js_model/model_test.dart
+++ b/tests/compiler/dart2js/js_model/model_test.dart
@@ -15,7 +15,15 @@ import '../serialization/helper.dart';
 
 const Map<String, String> SOURCE = const <String, String>{
   'main.dart': r'''
-main() {}
+foo({named}) => 1;
+bar(a) => !a;
+
+main() {
+  foo();
+  bar(true);
+  [];
+  {};
+}
 '''
 };