Adding supported checks for getCssCanvasContext.

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');
 
-  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);
+  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', () {
     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);
     });
 
     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);
     });
   });
 }