Fix 6397736: Swipe up to search layout fixes

This fixes several layout issues on phones and tablets with MultiWaveView.

It adds a new background scrim to be shown behind the MultiWaveView
on the navigation bar.

MultiWaveView is updated to handle gravity constraints which makes layouts
much more flexible across devices.

Change-Id: I64068f4eaa81ef6c464247049117d53432fcacbd