The attached patch adds a missing clampNegativeToZero() call to stop PlatformScrollBarGtk from allocating negative width and/or height for widgets.
This stops massive barfage of warnings like this on, for example, the Acid3 test:
(juniper:12951): Gtk-WARNING **: gtk_widget_size_allocate(): attempt to allocate widget with width -15 and height 15
Created attachment 20024 [details]
prevent PlatformScrollBarGtk from allocating negative width and/or height for widgets
Landed in r31399.
Including the bug URL/subject in the ChangeLog entry is a good idea for future patches. I also removed the comment since it's self-explanatory.