I forgot to assign this issue to the CL fixing it that just landed: https://crrev.com/c/1409738

I was unable to obtain the precise timings used in the NTP so I eyeballed a close match. There are also some complications in animating a variable size diff that I couldn't perfectly address. Nonetheless I think the final result is more than adequate.

I'm copying below the commit message and marking this as fixed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/69a484dacdbee8dafa040d31b38e144301be7e83

commit 69a484dacdbee8dafa040d31b38e144301be7e83
Author: Carlos Knippschild <carlosk@chromium.org>
Date: Wed Jan 16 00:29:12 2019

Animate hide/show transitions of dino page offline content list.

This change adds animation to the offline content list on the dino page
feature. This animation mimics the show/hide animation of the suggested
articles list presented in the NTP.

This also animates the initial population of the list when the dino
page is loaded.

Bug: 852872
Change-Id: Ief7295c41e53d71466619f9fd22651e365717799
Reviewed-on: https://chromium-review.googlesource.com/c/1409738
Commit-Queue: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Cathy Li <chili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622922}
[modify] https://crrev.com/69a484dacdbee8dafa040d31b38e144301be7e83/components/neterror/resources/neterror.css
[modify] https://crrev.com/69a484dacdbee8dafa040d31b38e144301be7e83/components/neterror/resources/neterror.html
[modify] https://crrev.com/69a484dacdbee8dafa040d31b38e144301be7e83/components/neterror/resources/neterror.js