In some cases, when rendering frame svg background, measures & margins
do not correspond to `enabledBorders`. I.e. `bottomHeight` may be equal to 5,
but the bottom border is disabled. This causes visual artifacts like this
{F5878318, layout=center, size=full}
//Pay close attention to the bottom of the Task switcher. It has a transparent strip at the bottom, which shouldn't be there.//
There are several approaches to fix this problem:
* Rewrite the `contentGeometry` method, so it takes into account whether
the left/top/right/bottom border is enabled.
* Or, call `updateSizes` before rendering frame svg background.
I took the latter approach in this diff.
Just for reference, this is "after"
{F5878319, layout=center, size=full}
BUG: 382324
BUG: 390632
BUG: 391659