This issue is happening because the foreground DownloadNotificationService is getting unexpectedly restarted and not stopped again. 

More specifically that "notifyDownloadPuased" is called multiple times, once propagated through DownloadBroadcastReceiver when the user interacts with the notification and another time through SystemDownloadNotifier, presumably through propagation by the native (debugging logs: https://paste.googleplex.com/6577383289126912). 

This is similar to the other issue that was seen related to offline pages restarting the foreground service after it was stopped already and then not shutting down the service again, in that case after notifyDownloadFailed shuts down the foreground service, notifyDownloadCanceled is called which accidentally starts but does not stop the service (crbug.com/776998). 

I have written a CL so that the user experience is as intended, but wonder if there's a larger problem where offline pages is altering the foreground service logic unknowingly by making multiple calls.

jming@, could you please add the OS for this bug ?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/16b84d67c1349f534233cecefc332cf94387542a

commit 16b84d67c1349f534233cecefc332cf94387542a
Author: Joy Ming <jming@chromium.org>
Date: Wed Nov 15 22:15:00 2017

Fix bug where notification for paused download persists.

There was a bug where the notification for a paused offline page would
persist even after swiped away. This is because in some cases, the
foreground download notification service is restarted after the download
was paused but it does not get shut down again so downloads remains in
the foreground. This CL fixes this by putting in a check that will check
to stop the service if it is accidentally restarted.

Bug:  784602 
Change-Id: Ic521fe39db62b3a0028ac3bed788f521cf0dcb44
Reviewed-on: https://chromium-review.googlesource.com/769869
Commit-Queue: Joy Ming <jming@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516853}
[modify] https://crrev.com/16b84d67c1349f534233cecefc332cf94387542a/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
[modify] https://crrev.com/16b84d67c1349f534233cecefc332cf94387542a/chrome/android/javatests/src/org/chromium/chrome/browser/download/DownloadNotificationServiceTest.java
[modify] https://crrev.com/16b84d67c1349f534233cecefc332cf94387542a/chrome/android/javatests/src/org/chromium/chrome/browser/download/MockDownloadNotificationService.java

This bug requires manual review: M63 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Please verify the fix in the next canary

Link to video: https://drive.google.com/open?id=1IMm7pOOeU--ggsPCfjibjg_Dt32OWxhe.
This change is not in the latest Canary yet, will verify tomorrow.

Jming@ Thanks for providing the video to verify the issue. We don't have access to view the video, but I verified the issue as per your steps provided in the issue.
Build: M64-64.0.3270.2 
Device: Pixel Xl O device

NOTE: This problem only happens when chrome://flags#enable-downloads-foreground is disabled. The flag should be disabled by default on Beta but enabled by default on Canary.

Merge approved! please verify the fix after merging on branch 3239.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b67a9c84106a77022afe4bb77c44f5e4890fd153

commit b67a9c84106a77022afe4bb77c44f5e4890fd153
Author: Joy Ming <jming@chromium.org>
Date: Fri Nov 17 23:26:26 2017

Fix bug where notification for paused download persists.

There was a bug where the notification for a paused offline page would
persist even after swiped away. This is because in some cases, the
foreground download notification service is restarted after the download
was paused but it does not get shut down again so downloads remains in
the foreground. This CL fixes this by putting in a check that will check
to stop the service if it is accidentally restarted.

Bug:  784602 
Change-Id: Ic521fe39db62b3a0028ac3bed788f521cf0dcb44
Reviewed-on: https://chromium-review.googlesource.com/769869
Commit-Queue: Joy Ming <jming@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#516853}(cherry picked from commit 16b84d67c1349f534233cecefc332cf94387542a)
Reviewed-on: https://chromium-review.googlesource.com/777405
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/branch-heads/3239@{#534}
Cr-Branched-From: adb61db19020ed8ecee5e91b1a0ea4c924ae2988-refs/heads/master@{#508578}
[modify] https://crrev.com/b67a9c84106a77022afe4bb77c44f5e4890fd153/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
[modify] https://crrev.com/b67a9c84106a77022afe4bb77c44f5e4890fd153/chrome/android/javatests/src/org/chromium/chrome/browser/download/DownloadNotificationServiceTest.java
[modify] https://crrev.com/b67a9c84106a77022afe4bb77c44f5e4890fd153/chrome/android/javatests/src/org/chromium/chrome/browser/download/MockDownloadNotificationService.java

Please verify the fix and close the bug if everything looks good!

Works as per expected behavior, Issue Verified in Pixel/O on 63.0.3239.60
Also verified M64-64.0.3270.2 as per C#10, hence closing the status.