The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/37d150002f3144ae2181316a11d4c76b92beaab5

commit 37d150002f3144ae2181316a11d4c76b92beaab5
Author: Kent Tamura <tkent@chromium.org>
Date: Tue Aug 28 07:16:26 2018

Forms: Add a UseCounter for a LEGEND quirk behavior

Bug:  878220 
Bug: https://github.com/whatwg/html/issues/3950
Change-Id: Ia0d53411b9dbeb15555ed66bf7539d3fd3fdd509
Reviewed-on: https://chromium-review.googlesource.com/1192367
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586606}
[modify] https://crrev.com/37d150002f3144ae2181316a11d4c76b92beaab5/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/37d150002f3144ae2181316a11d4c76b92beaab5/third_party/blink/renderer/core/html/forms/html_legend_element.cc
[modify] https://crrev.com/37d150002f3144ae2181316a11d4c76b92beaab5/tools/metrics/histograms/enums.xml

The NextAction date has arrived: 2018-10-30