Implement JsMethodMirror.constructorName.

dart/tests/lib/mirrors/constructors_test.dart

Index: dart/tests/lib/mirrors/constructors_test.dart
diff --git a/dart/tests/lib/mirrors/constructors_test.dart b/dart/tests/lib/mirrors/constructors_test.dart
index 89fc874786241e38946ea1d13ec519ae94374f7a..b42472f20164bc57a342434b9e3a170f2611d4bc 100644
--- a/dart/tests/lib/mirrors/constructors_test.dart
+++ b/dart/tests/lib/mirrors/constructors_test.dart
@@ -52,4 +52,14 @@ main() {
   for (var constructor in bizConstructors.values) {
     expect('[]', constructor.parameters);
   }
+
+  expect('[s()]',
+         fooConstructors.values.map((m) => m.constructorName).toList());
+  expect('[s()]',
+         barConstructors.values.map((m) => m.constructorName).toList());
+  expect('[s(named)]',
+         bazConstructors.values.map((m) => m.constructorName).toList());
+  expect('[s(), s(named)]',
+         bizConstructors.values.map((m) => m.constructorName).toList()
+             ..sort(compareSymbols));
 }