The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2f7c300938181c755792fdbcd2cadff9c38add55

commit 2f7c300938181c755792fdbcd2cadff9c38add55
Author: Joy Ming <jming@chromium.org>
Date: Thu Aug 10 22:27:37 2017

Fix bug where notification opens downloads home instead of offline page.

When a download is successful, a notification is shown. Before this CL,
when the download notification is clicked, the downloads home is opened.
After this CL, when the notification is clicked, the offlined page is
opened, if it's available.

Bug:  753887 ,753740,753710,753709
Change-Id: I6d4216ff998ca19b62780a52b0b122374f3ae82a
Reviewed-on: https://chromium-review.googlesource.com/609301
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Joy Ming <jming@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493569}
[modify] https://crrev.com/2f7c300938181c755792fdbcd2cadff9c38add55/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationFactory.java
[modify] https://crrev.com/2f7c300938181c755792fdbcd2cadff9c38add55/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
[modify] https://crrev.com/2f7c300938181c755792fdbcd2cadff9c38add55/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadUpdate.java