This task will additionally take care of attempts during which Chrome was killed (by OS, crashed or swiped away by the user).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb86cbdb812080c795bef2b2b21089d30c1797fc

commit cb86cbdb812080c795bef2b2b21089d30c1797fc
Author: fgorski <fgorski@chromium.org>
Date: Tue May 16 22:45:09 2017

[Offline pages] Reporting completed attempt when Chrome is killed

* Adds new Offliner::RequestStatus::BROWSER_KILLED.
* Reports UMA for requests updated in reconcile task with the status
  above.

BUG= 705115 
R=petewil@chromium.org

Review-Url: https://codereview.chromium.org/2883413002
Cr-Commit-Position: refs/heads/master@{#472233}

[modify] https://crrev.com/cb86cbdb812080c795bef2b2b21089d30c1797fc/components/offline_pages/core/background/offliner.h
[modify] https://crrev.com/cb86cbdb812080c795bef2b2b21089d30c1797fc/components/offline_pages/core/background/request_coordinator.cc
[modify] https://crrev.com/cb86cbdb812080c795bef2b2b21089d30c1797fc/tools/metrics/histograms/enums.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/16c45c04cf239a0153842f93c9fa7b5810d0233e

commit 16c45c04cf239a0153842f93c9fa7b5810d0233e
Author: fgorski <fgorski@chromium.org>
Date: Wed May 17 00:45:01 2017

[Offline pages] Reporting correct expiration reason in CleanupTask

BUG= 705115 

Review-Url: https://codereview.chromium.org/2882213003
Cr-Commit-Position: refs/heads/master@{#472269}

[modify] https://crrev.com/16c45c04cf239a0153842f93c9fa7b5810d0233e/components/offline_pages/core/background/cleanup_task.cc
[modify] https://crrev.com/16c45c04cf239a0153842f93c9fa7b5810d0233e/components/offline_pages/core/background/cleanup_task.h