Rename context2d to context2D.

tests/html/canvas_test.dart

Index: tests/html/canvas_test.dart
diff --git a/tests/html/canvas_test.dart b/tests/html/canvas_test.dart
index 475d20bb82e2a8171dc7061c414eee535b1f7eac..65b6493591f19f09a4e28f49671fc03a7e98bef5 100644
--- a/tests/html/canvas_test.dart
+++ b/tests/html/canvas_test.dart
@@ -12,7 +12,7 @@ main() {
   canvas = new CanvasElement(width:width, height:height);
   document.body.nodes.add(canvas);
 
-  context = canvas.context2d;
+  context = canvas.context2D;
 
   useHtmlConfiguration();
   test('CreateImageData', () {
@@ -32,7 +32,7 @@ main() {
   if (false)
   test('toDataUrl', () {
     var canvas = new CanvasElement(width: 100, height: 100);
-    var context = canvas.context2d;
+    var context = canvas.context2D;
     context.fillStyle = 'red';
     context.fill();