Change the way we generate stable id for DashboardSummary

- The countItem() method generates id based on position of Tile. This is
not truely stable.
- Added stable id constants for static views, and use hash of title as
stable id for tiles.

Bug: 33861822
Test: robotests
Change-Id: Ibbc88c82655503dc3964cb0c430c779dc9c93d41