Exposing DOM float & double types as double rather than num.

tests/html/instance_of_test.dart

Index: tests/html/instance_of_test.dart
diff --git a/tests/html/instance_of_test.dart b/tests/html/instance_of_test.dart
index 6e70809e6f051850bfdc88edd1b6cdc10aec9350..43542e859c5606a10c27f40611c1bd5698135ad2 100644
--- a/tests/html/instance_of_test.dart
+++ b/tests/html/instance_of_test.dart
@@ -42,9 +42,8 @@ main() {
     expect(context, isNot(isImageData));
     // expect(context, isNot(isCanvasPixelArray));
 
-    // 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.toDouble(),
+                                        canvas.height.toDouble());
     expect(image, isNot(isCanvasRenderingContext));
     expect(image, isNot(isCanvasRenderingContext2D));
     expect(image, isNot(isElement));