I believe this is a fairly easy fix. The problem is the line at [1] which causes the unnecessary animation. IIUC, this line was relevant when there were different extensions and apps subpages. This is no longer the case, so I think I can just delete that line.

@scottchen: Let me know if that sounds reasonable.

https://cs.chromium.org/chromium/src/chrome/browser/resources/md_extensions/manager.js?l=446

The original CL that introduced animateCurrentView() is at https://chromium-review.googlesource.com/c/chromium/src/+/619587, and it seems to validate my theory.

Posting before after screencasts. CL candidate is at https://chromium-review.googlesource.com/c/chromium/src/+/802141.

Deleted: unwanted_fade.mp4 423 KB

	unwanted_fade.mp4 423 KB View Download

Deleted: no_fade.mp4 289 KB

	no_fade.mp4 289 KB View Download

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/05f8ea6608884a96bc9be421ef8c5f23afee51a1

commit 05f8ea6608884a96bc9be421ef8c5f23afee51a1
Author: dpapad <dpapad@chromium.org>
Date: Thu Nov 30 23:48:57 2017

MD Extensions: Remove unnecessary fade-in/out when options dialog opens/closes.

The extra animation was introduced at crrev.com/c/619587, where at the time the
code was simulating a transition between the apps and extensions pages (which
were implemented as as a single page). This animation is no longer necessary and
in fact causes the problem when opening the in-page options dialog.

Bug:  776507 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ifd94b447b17673c04dfe227d1bd3d70bc87e3870
Reviewed-on: https://chromium-review.googlesource.com/802141
Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520753}
[modify] https://crrev.com/05f8ea6608884a96bc9be421ef8c5f23afee51a1/chrome/browser/resources/md_extensions/manager.js
[modify] https://crrev.com/05f8ea6608884a96bc9be421ef8c5f23afee51a1/chrome/browser/resources/md_extensions/view_manager.js