Cannot repro the issue. I only see one entry in downloads home, and I think that's expected as the download is created in step 4.

Is there any particular site you are seeing this?

All sites, I'm attaching video where steps are even more simple & you can see link one entry is disappearing after second kill for browser.

Deleted: video.mp4 6.6 MB

	video.mp4 6.6 MB View Download

Tested the issue in Android and able to reproduce the issue. 

Steps Followed:
1. Launched the Chrome Browser in Offline mode.
2. Navigate to any URL. Eg.: www.facebook.com
3. Tap on "DOWNLOAD WHEN ONLINE" button.
4. Kill the Chrome browser.
5. Launch the browser.
6. Tap on "DOWNLOAD WHEN ONLINE" button.
7. Tap on "CANCEL" button for the alert "Do you want to start downloading..... again?"
8. Tap on Chrome menu >> Downloads
9. Observed that there are two downloading bars for the same website. And when tried to tap on 'X' for one of the downloads, it won't respond.

Chrome versions tested:
66.0.3334.0(Canary)

OS:
Android 8.1.0

Android Devices:
Pixel 

Using the per-revision bisect providing the bisect results,
Good Build - 66.0.3328.0 (530801)
Bad Build - 66.0.3331.0 (531794)  

You are looking for a change made after 531607(GOOD), but before 531608(BAD).

CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
https://chromium.googlesource.com/chromium/src/+/dfcd80b7fd147508393a742b9402ab92c483d7d8

From the CL above, assigning the issue to the owner concerned.

@dimich:  Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to owner concerned.

Please navigate to below link for log's and video--
go/chrome-androidlogs/806617

Note: This issue is not observed in Desktop.

Regressed recently, tagging as RBS. Please feel free to remove if needed.

The patch indicated in #6 is indeed a culprit. 

The patch that will fix this is in code review: https://chromium-review.googlesource.com/c/chromium/src/+/896553

 Issue 808502  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e82cd1b3d7789fa734e96b6d24de6be757d619eb

commit e82cd1b3d7789fa734e96b6d24de6be757d619eb
Author: Dmitry Titov <dimich@chromium.org>
Date: Tue Feb 06 20:46:11 2018

Remove AreItemsAvailable and OnIntemsAvailable from OfflineItemsProvider interface.

This simplifies interface, OfflineItemsAggregator impl and is another step away from
loading all the items on startup and rather loading/caching them transparently as
needed.

Next steps:
- remove GetItemById as not used.
- consider unloading items from memory/caches using a new method, like ClearCaches().

Bug:  806617 
Change-Id: Ife57fa13e72273a6bac9b4e843a131f7c9c8de15
Reviewed-on: https://chromium-review.googlesource.com/896553
Reviewed-by: vitaliii <vitaliii@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Commit-Queue: Dmitry Titov <dimich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534788}
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/chrome/android/java/src/org/chromium/chrome/browser/download/items/OfflineContentAggregatorNotificationBridgeUi.java
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadHistoryAdapter.java
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/chrome/android/javatests/src/org/chromium/chrome/browser/download/ui/StubbedProvider.java
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/chrome/android/junit/src/org/chromium/chrome/browser/download/items/OfflineContentAggregatorNotificationBridgeUiTest.java
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/chrome/browser/background_fetch/background_fetch_delegate_impl.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/chrome/browser/background_fetch/background_fetch_delegate_impl.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider_unittest.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/android/java/src/org/chromium/components/offline_items_collection/OfflineContentAggregatorBridge.java
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/android/java/src/org/chromium/components/offline_items_collection/OfflineContentProvider.java
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/android/offline_content_aggregator_bridge.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/android/offline_content_aggregator_bridge.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/offline_content_aggregator.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/offline_content_aggregator.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/offline_content_aggregator_unittest.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/offline_content_provider.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/test_support/mock_offline_content_provider.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/test_support/mock_offline_content_provider.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/throttled_offline_content_provider.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/throttled_offline_content_provider.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_items_collection/core/throttled_offline_content_provider_unittest.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_pages/core/downloads/download_ui_adapter.cc
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_pages/core/downloads/download_ui_adapter.h
[modify] https://crrev.com/e82cd1b3d7789fa734e96b6d24de6be757d619eb/components/offline_pages/core/downloads/download_ui_adapter_unittest.cc

Seems to be fixed with latest Canary

This issue is marked as a release blocker with no milestone associated. Please add an appropriate milestone.

All release blocking issues should have milestones associated to it, so that the issue can tracked and the fixes can be pushed promptly.

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Fixed before M66 branch point, no follow up action necessary.

Issue 807943 has been merged into this issue.