The EngagementDetails struct allows consumers to determine if
a particular origin is added to home screen. The querying is
equivalent to that implemented in Important Sites - both use a 10 day
recency cutoff. All recently launched sites are recorded by the
engagement service at the exact same time as the content setting used by
the Important Sites code.

This CL removes the custom querying for installed state in Important
Sites and simply checks the EngagementDetails struct.

BUG=711041

Change-Id: I7747f0fbd08e6912cc5966f3ced678b717114547
Reviewed-on: https://chromium-review.googlesource.com/765555


Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516111}