Fix <select>s on about:flags with big font sizes

R=rbpotter@chromium.org
BUG=964906

Change-Id: I031fd80a4513cc2b99164ad10a10cafd364642b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625848
Commit-Queue: Dan Beam <dbeam@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Auto-Submit: Dan Beam <dbeam@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662950}

components/flags_ui/resources/flags.css

@@ -313,7 +313,7 @@ select {
   border: 1px solid var(--link-color);
   color: var(--link-color);
   font-size: .8125rem;
-  height: 26px;
+  height: 1.625rem;
   letter-spacing: .01em;
   max-width: 150px;
   text-align-last: center;