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- We currently prune out cancelled and non-resumable failed/interrupted
downloads from downloads home.  In the V2 version this didn't happen, so
this adds the filter to address this.

- In the process of adding the filter, I realized that the filter's
onItemUpdated() logic does not handle items updating to/from a filtered
out state.  So this also adds that support as well as tests for it.

BUG=889213

Change-Id: I5ae6b836abf77f914bd3f106a2d21b015e03aad2
Reviewed-on: https://chromium-review.googlesource.com/1244123
Commit-Queue: David Trainor <dtrainor@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595671}