IMGUIContainer in ScrollView causes flickering

Some flickering occurs when having IMGUIContainers in the scrollview. This is likely caused by the fact that now the layout of scrollview is performed in multiple frames (see https://fogbugz.unity3d.com/f/cases/1417765) and https://ono.unity3d.com/unity/unity/pull-request/144736/_/uitools/fix-1417765).

 

 

Steps:

1 - Create a document

2 - Select the Root item in the Hierarchy pane

3 - Resize the UI Builder window to squeeze the inspector to a really small height to display the Scrollbars

4 - Enlarge the UI Builder window bit by bit a couple of times

Actual outcome:

The flickering happens