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

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 97f6119f69bdd3b0a0edf53ff877f0afed0a0797..fda5e3ef1449498ed6f387608644b27a93bbb6d0 100644
--- a/tests/html/canvas_test.dart
+++ b/tests/html/canvas_test.dart
@@ -16,8 +16,8 @@ main() {
 
   useHtmlConfiguration();
   test('CreateImageData', () {
-    ImageData image = context.createImageData(canvas.width,
-                                              canvas.height);
+    ImageData image = context.createImageData(canvas.width.toDouble(),
+                                              canvas.height.toDouble());
     List<int> data = image.data;
 
     expect(data, hasLength(40000));