Note that the icon_20px screenshot is not 100% correct. The text on the 2nd line needs more left margin to still align with the top row's text.

20x20 LGTM. And yes, alignment of the text as suggest in c1 is preferred 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0329d2ee7386116319558fa7d0de9d163ac35b0f

commit 0329d2ee7386116319558fa7d0de9d163ac35b0f
Author: Esmael El-Moslimany <aee@chromium.org>
Date: Tue Feb 27 04:13:50 2018

MD Extensions: in keboard shortcuts extensions settings, set extension
    icon size to 20x20, align text

Bug:  794275 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ib7bdaf43dce5074c4b758d27ae47afb54b1d2750
Reviewed-on: https://chromium-review.googlesource.com/937961
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539399}
[modify] https://crrev.com/0329d2ee7386116319558fa7d0de9d163ac35b0f/chrome/browser/resources/md_extensions/keyboard_shortcuts.html

Able to reproduce this issue on build without fix(observed small icon for extension), hence verifying the fix on latest canary 66.0.3357.0 using Mac 10.13.3, Windows 10 and Ubuntu 14.04.

Observing bigger icon when compared to build without fix. Attaching screenshots for reference.

Hence adding Verified labels.

Deleted: Build with fix.png 12.1 KB

	Build with fix.png 12.1 KB View Download

Deleted: Build without fix.png 12.1 KB

	Build without fix.png 12.1 KB View Download