Adding supported checks for Element.matches.

tests/html/element_test.dart

Index: tests/html/element_test.dart
diff --git a/tests/html/element_test.dart b/tests/html/element_test.dart
index d849731461416dd145b009b2f5ec86b0b6fa0bf7..80103cf136e7d52237e0545d78500ca19054d587 100644
--- a/tests/html/element_test.dart
+++ b/tests/html/element_test.dart
@@ -596,14 +596,23 @@ main() {
     });
   });
 
+  group('supported_matches', () {
+    test('supported', () {
+      expect(Element.supportsMatches, true);
+    });
+  });
+
   group('matches', () {
     test('matches', () {
-      var element = new DivElement();
-      element.classes.add('test');
-
-      expect(element.matches('div'), true);
-      expect(element.matches('span'), false);
-      expect(element.matches('.test'), true);
+      var expectation = Element.supportsMatches ? returnsNormally : throws;
+      expect(() {
+        var element = new DivElement();
+        element.classes.add('test');
+
+        expect(element.matches('div'), true);
+        expect(element.matches('span'), false);
+        expect(element.matches('.test'), true);
+      }, expectation);
     });
   });