load MutationObserver polyfill for IE

pkg/template_binding/test/template_binding_test.dart

Index: pkg/template_binding/test/template_binding_test.dart
diff --git a/pkg/template_binding/test/template_binding_test.dart b/pkg/template_binding/test/template_binding_test.dart
index d43e36b426f40ff4fe1df4da00d50c4335a145af..cc52811e8fbc5f2498e1ec9d101d757dbb4066ac 100644
--- a/pkg/template_binding/test/template_binding_test.dart
+++ b/pkg/template_binding/test/template_binding_test.dart
@@ -27,15 +27,25 @@ import 'utils.dart';
 main() {
   useHtmlConfiguration();
 
-  setUp(() {
+  // Load MutationObserver polyfill in case IE needs it.
+  var script = new ScriptElement()
+      ..src = '/root_dart/pkg/mutation_observer/lib/mutation_observer.min.js';
+  var polyfillLoaded = script.onLoad.first;
+  document.head.append(script);
+
+  setUp(() => polyfillLoaded.then((_) {
     document.body.append(testDiv = new DivElement());
-  });
+  }));
 
   tearDown(() {
     testDiv.remove();
     testDiv = null;
   });
 
+  test('MutationObserver is supported', () {
+    expect(MutationObserver.supported, true, reason: 'polyfill was loaded.');
+  });
+
   group('Template Instantiation', templateInstantiationTests);
 
   group('Binding Delegate API', () {