Partial fix for LT-583 "Sidebar loses tool list"

This fixes the case where the user resizes Flex, but not via
maximize. Maximize requires restoring and then re-maximizing
to work right. It seems the EnsureVisible call is satisfied it is
visible, even if one pixel is showing of the item.

Change-Id: I17d9afe47b9b4d887531b35717952a7d7a6e3838