device_state: heuristically removing duplicate states
device_state: heuristically removing duplicate states

Currently DroidBot considers all views when generating the
hash string for a state, causing visually equal states to
have different different strings in some cases.

This commit removes duplicate views by selecting the down-most
one when they have same view rectangles.

Signed-off-by: Ziyue Yang <ae4c3d0b1e2eac22fa7c83b3d8288f59ae63213d@hotmail.com>

nastya/droidbot,honeynet/droidbot,honeynet/droidbot,honeynet/droidbot,nastya/droidbot,honeynet/droidbot,lynnlyc/droidbot,nastya/droidbot,nastya/droidbot,lynnlyc/droidbot