Revert "Remove Object.dynamic."

tests/html/instance_of_test.dart

 #library('InstanceOfTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   CanvasElement canvas;
 
   canvas = new Element.tag('canvas');
   canvas.attributes['width'] = 100;
@@ skipping 11 matching lines @@
 
     CanvasRenderingContext2D context = canvas.getContext('2d');
     Expect.isTrue(context is CanvasRenderingContext);
     Expect.isTrue(context is CanvasRenderingContext2D);
     Expect.isFalse(context is Element);
     Expect.isFalse(context is CanvasElement);
     Expect.isFalse(context is ImageData);
     // Expect.isFalse(context is CanvasPixelArray);
 
     // FIXME(b/5286633): Interface injection type check workaround.
-    var image = context.createImageData(canvas.width as Dynamic,
-                                        canvas.height as Dynamic);
+    var image = context.createImageData(canvas.width.dynamic, canvas.height.dynamic);
     Expect.isFalse(image is CanvasRenderingContext);
     Expect.isFalse(image is CanvasRenderingContext2D);
     Expect.isFalse(image is Element);
     Expect.isFalse(image is CanvasElement);
     Expect.isTrue(image is ImageData);
     // Expect.isFalse(image is CanvasPixelArray);
 
     // Include CanvasPixelArray since constructor and prototype are not
     // available until one is created.
     var bytes = image.data;
     Expect.isFalse(bytes is CanvasRenderingContext);
     Expect.isFalse(bytes is CanvasRenderingContext2D);
     Expect.isFalse(bytes is Element);
     Expect.isFalse(bytes is CanvasElement);
     Expect.isFalse(bytes is ImageData);
     Expect.isTrue(bytes is Uint8ClampedArray);
 
     // FIXME: Ensure this is an SpanElement when we next update
     // WebKit IDL.
     var span = new Element.tag('span');
     Expect.isTrue(span is Element);
   });
 }