Making a window with certain widgets smaller doesn't work on Ubuntu 18.04 and 20.04

Description When resizing a window of an application containing a WebView or a MultilineTextInput widget, making it bigger works, but making it smaller doesn’t work. Neither horizontally nor vertically. Note that only a few widgets seem to prevent shrinking, e.g. the window of the hello world tutorial application works fine.

To Reproduce

1. Set up an Ubuntu 18.04 or 20.04 development environment (e.g. using https://github.com/rknuus/toga-dependency-verification).
2. Start the browser app of the tutorial.
3. Resize the window, particularly try to make it smaller.

Expected behavior The window size changes in both directions.

Environment:

• Operating System:
  • Ubuntu 18.04 with GTK+ version 3.22.30-1ubuntu4 of libgtk-3-0 and version 2.24-32-1ubuntu1 of libgtk2.0-0
  • Ubuntu 20.04 with GTK+ version 3.24-20-0ubuntu1 of libgtk-3-0 and version 2.24-32-4ubuntu4 of libgtk2.0-0
• Python version: 3.6.9 on Ubuntu 18.04 resp. 3.8.5 on Ubuntu 20.04
• Software versions:
  • Toga: 0.3.0.dev26

[rknuus]

Perhaps my problem description was not accurate, my apologies.

I understand that certain widgets have some minimal space requirements. My issue is, that starting from the default size I can make the window bigger, but then I can never make it smaller again, even though the window is now bigger than it was initially, i.e. making it a bit smaller should not violate the minimal space requirements.

[MuhammadMouradG]

This bug needs some work my #1224 PR will not solve it perfectly.