The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/25fd471cd71b05e6ec1413285d3c0679e3409ce6

commit 25fd471cd71b05e6ec1413285d3c0679e3409ce6
Author: Scott Chen <scottchen@chromium.org>
Date: Fri Jul 27 19:21:09 2018

MD select: makes dropdown arrow smaller.

This CL makes MD select's dropdown arrow more similarly sized with other
icons. It also makes the dropdown arrow not scale with font-size, since
other icons don't do that either.

Bug:  867185 
Change-Id: Iedcce94c126fecd0284c1dc3d2485d3048039992
Reviewed-on: https://chromium-review.googlesource.com/1150564
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578744}
[modify] https://crrev.com/25fd471cd71b05e6ec1413285d3c0679e3409ce6/ui/webui/resources/html/md_select_css.html