Fix to distingish Document from HtmlDocument on ie9

tests/html/document_test.dart

Index: tests/html/document_test.dart
diff --git a/tests/html/document_test.dart b/tests/html/document_test.dart
index 2a543e751e63faaa64ebcd8bf2b6961a4a1b5a13..355a126e85a5939b927f1b65b4c64e91778b2653 100644
--- a/tests/html/document_test.dart
+++ b/tests/html/document_test.dart
@@ -13,6 +13,8 @@ main() {
   var isUnknownElement =
       predicate((x) => x is UnknownElement, 'is UnknownElement');
 
+  var inscrutable;
+
   test('CreateElement', () {
     // FIXME: nifty way crashes, do it boring way.
     expect(new Element.tag('span'), isElement);
@@ -42,6 +44,8 @@ main() {
   });
 
   group('document', () {
+    inscrutable = (x) => x;
+
     test('Document.query', () {
       Document doc = new DomParser().parseFromString(
       '''<ResultSet>
@@ -80,5 +84,23 @@ main() {
       doc.body.nodes.add(div2);
       expect(doc.query('#foo').text, 'bar');
     });
+
+    test('typeTest1', () {
+      inscrutable = inscrutable(inscrutable);
+      var doc1 = document;
+      expect(doc1 is HtmlDocument, true);
+      expect(inscrutable(doc1) is HtmlDocument, true);
+      var doc2 = document.implementation.createHtmlDocument('');
+      expect(doc2 is HtmlDocument, true);
+      expect(inscrutable(doc2) is HtmlDocument, true);
+    });
+
+    test('typeTest2', () {
+      inscrutable = inscrutable(inscrutable);
+      // XML document.
+      var doc3 = document.implementation.createDocument(null, 'report', null);
+      expect(doc3 is HtmlDocument, false);
+      expect(inscrutable(doc3) is HtmlDocument, false);
+    });
   });
 }