Adding supported checks for getCssCanvasContext.

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 eb5d36398fe9e39928d31080a408c6db57fb2ccf..fece53edeb88ec190262a1557e2db16633a76591 100644
--- a/tests/html/document_test.dart
+++ b/tests/html/document_test.dart
@@ -13,12 +13,31 @@ main() {
   var isUnknownElement =
       predicate((x) => x is UnknownElement, 'is UnknownElement');
 
+  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 context = document.getCssCanvasContext('2d', 'testContext', 10, 20);
-      expect(context is CanvasRenderingContext2D, true);
-      expect(context.canvas.width, 10);
-      expect(context.canvas.height, 20);
+      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);
     });
   });