To reproduce:
1. Open a new Unity project
3. Switch to One Column Layout in the Project folder

Expected result: there should be a small tab on the bottom of the Project folder in which you can resize the assets and see the name and icon of the asset you click on.
Actual result: that tab does not exist in One Column Layout

Note: While in One Column Layout, write anything in the search bar - the tab on the bottom will appear.

Reproduced on: 5.5.4p1, 5.6.2f1, 2017.1.0b10, 2017.2.0a4

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I think the problem here is that we are showing the resize slider when searching in one-column mode.

By design: The reason why there's no resize slider and selected item info in One Column Layout mode it's because it should reflect a tree view. In this mode, the elements have fixed sizes in order to give a compact view.