Vaadin 8, Window opened with undefined height gets scrolled to the top on each poll

• Vaadin Framework version: 8.8.5
• Browser version:
  Chromium Version 76.0.3809.100 (Official Build) Built on Ubuntu , running on Ubuntu 16.04 (64-bit) (also reproduced with Firefox)
• Web container name and version: Tomcat 9.0
• Description of the bug:

I have created a Window with width 100%, and height undefined. This Window has more content than fits to the monitor, so a vertical scrollbar appears as it should.
When manually scrolling to the bottom, it automatically scrolls back to the top on each long poll.

• Expected behavior: There should be no inadverted scrolling.

• Actual behavior: Inadverted scroll.

Root cause:
VWindow.java:
@Override
public void setHeight(String height) {
// Override PopupPanel which sets the height to the contents
getElement().getStyle().setProperty("height", height); // scrolls to top, even if height remains ""
// Update v-has-height in case undefined window is resized
setStyleName("v-has-height", height != null && !height.isEmpty());
}

AbstractComponentConnector.updateComponentSize() just calls for size update, without checking if there is any size change, and a side effect of scrolling happens.

Workaround:
I set the window height to 100% instead of undefined, and it looks like solving the issue.

Start with VWindow.java#setHeight and AbstractComponentConnector.updateComponentSize(), following the issue's description of the size-update path. Reproduce the undefined-height Window case while scrolling, then verify that polling no longer moves the viewport to the top without changing the intended Window sizing behavior.