pine: Fix background of two overflow apps case

The outer box layout preferred size is calculated based on its children.
In the two overflow app case, on children has 0 preferred size so the
layout manager calculated 42x22. We add padding such that if there is
one inner box layout, the preferred size is 42x42.

Also modified some code so we don't create the inner bottom box layout
if it is not needed (2 overflow apps case).

Test: manual
Test: manually printed preferred sizes for 2 & 4 overflow apps
Change-Id: I333fbf1ebfe9303cd26095bb21f600f96f92af4d
Fixed: b:331215843
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5407255


Reviewed-by: Xiaodan Zhu <zxdan@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280938}