Printing WebView may results in empty page

We see regression after the fix for https://bugs.openjdk.java.net/browse/JDK-8260165 (https://github.com/openjdk/jfx/pull/408) has been applied in the following case:
1. a WebView (not shown in the Stage) is printed
2. its size is slightly altered (or some other minor change is applied),
3. the WebView is printed again. This results in an empty page.

At first glance, it looks to me that this is caused by the 250ms delay that is introduced in this PR. The problem didn't happen before this PR was merged.