Fix to distingish Document from HtmlDocument on ie9

tests/html/document_test.dart

 library DocumentTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlIndividualConfiguration();
 
   var isElement = predicate((x) => x is Element, 'is an Element');
   var isDivElement = predicate((x) => x is DivElement, 'is a DivElement');
   var isAnchorElement =
       predicate((x) => x is AnchorElement, 'is an AnchorElement');
   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);
     expect(new Element.tag('div'), isDivElement);
     expect(new Element.tag('a'), isAnchorElement);
     expect(new Element.tag('bad_name'), isUnknownElement);
   });
 
   group('supports_cssCanvasContext', () {
     test('supports_cssCanvasContext', () {
       expect(HtmlDocument.supportsCssCanvasContext, true);
     });
   });
 
   group('getCssCanvasContext', () {
     test('getCssCanvasContext 2d', () {
       var expectation = HtmlDocument.supportsCssCanvasContext ?
         returnsNormally : throws;
 
       expect(() {
         var context = document.getCssCanvasContext('2d', 'testContext', 10, 20);
         expect(context is CanvasRenderingContext2D, true);
         expect(context.canvas.width, 10);
         expect(context.canvas.height, 20);
       }, expectation);
     });
   });
 
   group('document', () {
+    inscrutable = (x) => x;
+
     test('Document.query', () {
       Document doc = new DomParser().parseFromString(
       '''<ResultSet>
            <Row>A</Row>
            <Row>B</Row>
            <Row>C</Row>
          </ResultSet>''','text/xml');
 
       var rs = doc.query('ResultSet');
       expect(rs, isNotNull);
@@ skipping 18 matching lines @@
 
     test('importNode', () {
       var div = new Element.html('<div><div id="foo">bar</div></div>');
       var doc = document.implementation.createHtmlDocument('');
       var div2 = doc.importNode(div, true);
       expect(div2, isNot(equals(div)));
       expect(div2.ownerDocument, doc);
       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);
+    });
   });
 }