[Downloads] Add support for tracking incomplete downloads

[Downloads] Add support for tracking incomplete downloads

* Start tracking most DownloadItems on the Java side, but
  display only completed downloads in the UI.

* Start monitoring for the creation of DownloadItems, which
  happens when new downloads are triggered.

* Change how deletion is done and undone:
  Instead of straight up removing items from the adapter,
  hide the DownloadItems from view until we are alerted that
  the downloads have been deleted by the backends.  This
  allows us to keep track and simplifies a few data structure
  interactions.

* Add proper support for monitoring changes to DownloadItems,
  and add functions for checking if updates should be
  communicated to the UI.

BUG=658246, 654630
Committed: https://crrev.com/13fa9f45a129fb1404d39b11e30fa911dbc534f8
Cr-Commit-Position: refs/heads/master@{#433287}

[gone, 2016-11-17 23:56:35]

dfalcantara@chromium.org changed reviewers:
+ qinmin@chromium.org, twellington@chromium.org

[gone, 2016-11-17 23:56:36]

Min for changes to DownloadManagerService

Theresa for all the other things and stuff

[gone, 2016-11-18 00:16:07]

The CQ bit was checked by dfalcantara@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-11-18 00:18:03]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[qinmin, 2016-11-18 19:06:12]

DownloadManagerService lgtm

[Theresa, 2016-11-18 19:25:51]

lgtm

[gone, 2016-11-18 19:27:00]

The CQ bit was checked by dfalcantara@chromium.org

[commit-bot: I haz the power, 2016-11-18 19:28:22]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-18 20:22:36]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-11-18 20:26:03]

Description was changed from

==========
[Downloads] Add support for tracking incomplete downloads

* Start tracking most DownloadItems on the Java side, but
  display only completed downloads in the UI.

* Start monitoring for the creation of DownloadItems, which
  happens when new downloads are triggered.

* Change how deletion is done and undone:
  Instead of straight up removing items from the adapter,
  hide the DownloadItems from view until we are alerted that
  the downloads have been deleted by the backends.  This
  allows us to keep track and simplifies a few data structure
  interactions.

* Add proper support for monitoring changes to DownloadItems,
  and add functions for checking if updates should be
  communicated to the UI.

BUG=658246,654630
==========

to

==========
[Downloads] Add support for tracking incomplete downloads

* Start tracking most DownloadItems on the Java side, but
  display only completed downloads in the UI.

* Start monitoring for the creation of DownloadItems, which
  happens when new downloads are triggered.

* Change how deletion is done and undone:
  Instead of straight up removing items from the adapter,
  hide the DownloadItems from view until we are alerted that
  the downloads have been deleted by the backends.  This
  allows us to keep track and simplifies a few data structure
  interactions.

* Add proper support for monitoring changes to DownloadItems,
  and add functions for checking if updates should be
  communicated to the UI.

BUG=658246,654630

Committed: https://crrev.com/13fa9f45a129fb1404d39b11e30fa911dbc534f8
Cr-Commit-Position: refs/heads/master@{#433287}
==========

[commit-bot: I haz the power, 2016-11-18 20:26:04]

Patchset 2 (id:??) landed as
https://crrev.com/13fa9f45a129fb1404d39b11e30fa911dbc534f8
Cr-Commit-Position: refs/heads/master@{#433287}