Always float toolbar to top of page, not last branch node

The check for the toolbar not overlapping the last branch node
'fixes' an edge case where the user has scrolled too far, and
the viewport is shorter than the last branch. A more common
problem caused by this is that if the last branch is very tall
the toolbar disappears whenever you scroll past it.

Bug: 48662
Change-Id: I1c7662f2b6f1ced6f80dec16c6ed69a8cc0c06c8
Merge "Always float toolbar to top of page, not last branch node"