Update layout make talkback first focus item is root button

Because chips layout parent is higher than tool bar, talkback
will focus on that layout child which is chip firstly. Change
layout parent space to margin let tool bar layout is highest
layout in this layer to fix this bug.

Fix: 124342125
Test: manual
Test: atest DocumentsUIGoogleTests
Change-Id: I1692b24a9ea305b4ea13db024b66e7d1f29039c9