A swipe control uses the same icon as the smaller one for mouse hover. ui/message_center/vector_icons/notification_snooze_button.icon
The resource has dedicated icons for 12 and 24 pixels.

It's scaled to 20px when displayed on the swipe controls.
https://cs.chromium.org/chromium/src/ash/system/message_center/message_center_style.h?q=kSwipeControlButtonImageSize&sq=package:chromium&g=0&l=25

Here are the screenshots with existing code and crrev.com/c/1379628.
I've found the smaller icon (mousehover) also has the same issue.

Deleted: before.png 10.3 KB

	before.png 10.3 KB View Download

Deleted: after.png 3.1 KB

	after.png 3.1 KB View Download

Screenshot with Patch Set 3.

Deleted: 2ndfix.png 2.8 KB

	2ndfix.png 2.8 KB View Download

Thanks a lot Yamaguchi!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dd3a21e77dfeae0ca1f3a59da404a8444df302a1

commit dd3a21e77dfeae0ca1f3a59da404a8444df302a1
Author: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Date: Tue Jan 08 03:15:32 2019

Update notification snooze icon.

The old icon looked asymmetric when rendered. This will affect the both
icons for mouse hover and swipe control.

BUG= 915436 
TEST=manual, screenshot pasted on the bug

Change-Id: I2ea31b2d7bd4ee720d11ef4077300544fecba12c
Reviewed-on: https://chromium-review.googlesource.com/c/1379628
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620598}
[modify] https://crrev.com/dd3a21e77dfeae0ca1f3a59da404a8444df302a1/ui/message_center/vector_icons/notification_snooze_button.icon