The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2e01255a4b3edd8d0d7f5e3d69cc8ea86026de79

commit 2e01255a4b3edd8d0d7f5e3d69cc8ea86026de79
Author: Joy Ming <jming@chromium.org>
Date: Mon Sep 11 22:07:48 2017

Re-launch completed notification during foreground switch.

This is part of the larger refactor to make downloads a foreground
service on all versions of Android. Before this CL, when a download was
completed and another download was in progress, the completed
notification would disappear. This was due to the fact that calling
startForeground on a different notification when there was already a
notification pinned to the foreground would cause the original
notification to be cancelled. This is fixed in later versions of Android
but for older versions, a hack that re-launches the notification during
the foreground switch is required.

Bug:  747563 , 759170 
Change-Id: I171ffa086d3d3c64843bfa3ae9b2737999b75520
Reviewed-on: https://chromium-review.googlesource.com/657242
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Joy Ming <jming@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501058}
[modify] https://crrev.com/2e01255a4b3edd8d0d7f5e3d69cc8ea86026de79/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadForegroundService.java
[modify] https://crrev.com/2e01255a4b3edd8d0d7f5e3d69cc8ea86026de79/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadForegroundServiceManager.java