Notification badges are only supported on Android.

chrome/browser/notifications/platform_notification_service_impl.cc

Index: chrome/browser/notifications/platform_notification_service_impl.cc
diff --git a/chrome/browser/notifications/platform_notification_service_impl.cc b/chrome/browser/notifications/platform_notification_service_impl.cc
index f8fdd5c9157c73a0c060cca3f2ddc5c8b740bd37..081922059852d42277f2571f853b44df0c78982d 100644
--- a/chrome/browser/notifications/platform_notification_service_impl.cc
+++ b/chrome/browser/notifications/platform_notification_service_impl.cc
@@ -469,10 +469,13 @@ Notification PlatformNotificationServiceImpl::CreateNotificationFromData(
   notification.set_renotify(notification_data.renotify);
   notification.set_silent(notification_data.silent);
 
+  // Badges are only supported on Android: crbug.com/591394#c4

[Peter Beverloo, 2016/05/23 15:40:03]

Can we summarize the reasoning here rather than link to the bug?

I'd also like to see a TODO here to make sure that
|notification_resources.badge| drawsNothing() on other platforms.

[Michael van Ouwerkerk, 2016/05/23 16:12:26]

Done.

+#if defined(OS_ANDROID)
   // TODO(peter): Handle different screen densities instead of always using the
   // 1x bitmap - crbug.com/585815.
   notification.set_small_image(
       gfx::Image::CreateFrom1xBitmap(notification_resources.badge));
+#endif  // defined(OS_ANDROID)
 
   // Developer supplied action buttons.
   std::vector<message_center::ButtonInfo> buttons;