Fix6398209: reveal search when home button is long-pressed

This change add a feature to reveal the swipe to search interface
when the home key is pressed for longer than 50ms.  It progressively
reveals the interface.  It still requires a bit of tuning, but all
the basic parameters are in this CL.

Change-Id: I1d3a5bb7b912265eb41da68bc9313eee1af2e415