Add test for calling emulated functions from JS

tests/html/js_test.dart

Index: tests/html/js_test.dart
diff --git a/tests/html/js_test.dart b/tests/html/js_test.dart
index e120895321461d7ff9bdb9ef9283fbc9cd7c1afb..facf3cb2e27a79fcc54f5bb459e357bb933f887e 100644
--- a/tests/html/js_test.dart
+++ b/tests/html/js_test.dart
@@ -201,6 +201,10 @@ class Color {
 
 class TestDartObject {}
 
+class Callable {
+  call() => 'called';
+}
+
 main() {
   _injectJs();
   useHtmlConfiguration();
@@ -460,7 +464,7 @@ main() {
 
   });
 
-  group('Dart callback', () {
+  group('Dart functions', () {
     test('invoke Dart callback from JS', () {
       expect(() => context.callMethod('invokeCallback'), throws);
 
@@ -498,6 +502,13 @@ main() {
       expect(result, 42);
     });
 
+    test('emulated functions should be callable in JS', () {
+      context['callable'] = new Callable();
+      var result = context.callMethod('callable');
+      expect(result, 'called');
+      context.deleteProperty('callable');
+    });
+
   });
 
   group('JsObject.jsify()', () {