The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fa1d66b71e30ce368fa536f21ccdbe266c634508

commit fa1d66b71e30ce368fa536f21ccdbe266c634508
Author: Kent Tamura <tkent@chromium.org>
Date: Wed Oct 10 02:29:56 2018

Add a bunch of UseCounters for rendered -webkit-appearance keywords

We'd like to decrease the number of the keywords of -webkit-appearance.
If kCSSValueApparance${kw}Rendered counter is small, we might be able to
remove the keyword or make the keyword UA-stylesheet-only. If
kCSSValueApparance${kw}ForOthersRendered is small, we might be able to
switch to 'auto' keyword.

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ie805349f835c2df1135fbc0a9f74a0d63a34c7d3
Bug:  892586 
Reviewed-on: https://chromium-review.googlesource.com/c/1272775
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598185}
[modify] https://crrev.com/fa1d66b71e30ce368fa536f21ccdbe266c634508/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/fa1d66b71e30ce368fa536f21ccdbe266c634508/third_party/blink/renderer/core/paint/theme_painter.cc
[modify] https://crrev.com/fa1d66b71e30ce368fa536f21ccdbe266c634508/tools/metrics/histograms/enums.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/13e5df88c1fd3b376eeb32dc15e46273f302b190

commit 13e5df88c1fd3b376eeb32dc15e46273f302b190
Author: Kent Tamura <tkent@chromium.org>
Date: Wed Oct 10 07:16:39 2018

Add a UseCounter for -webkit-appearance access via getComputedStyle().

This counts web-exposed getComputedStyle()["-webkit-appearance"],
getComputedStyle().webkitAppearance, and
getComputedStyle().getPropertyValue("-webkit-appearance"), but not count
-webkit-appearance access for DevTools style panel.

If the counter is very small,
 - We may drop keywords which can be parsed but can't be rendered.
 - We may drop a quirky behavior of getComputedStyle() for -webkit-appearance.
  It returns an effective appearance value, unlike other CSS properties.
  e.g. <style>button { background:green; }</style><button>Click</button>
   getComputedStyle(button).webkitAppearance returns "none" instead of "button".

Bug:  892586 
Change-Id: I626f23009dafd113e1ebf29a73b541264399de5f
Reviewed-on: https://chromium-review.googlesource.com/c/1272759
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598239}
[modify] https://crrev.com/13e5df88c1fd3b376eeb32dc15e46273f302b190/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/13e5df88c1fd3b376eeb32dc15e46273f302b190/third_party/blink/renderer/core/css/css_computed_style_declaration.cc
[modify] https://crrev.com/13e5df88c1fd3b376eeb32dc15e46273f302b190/tools/metrics/histograms/enums.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4b22f37270ca87b7d8f3c8c2a2eeabda9d10e6c5

commit 4b22f37270ca87b7d8f3c8c2a2eeabda9d10e6c5
Author: Kent Tamura <tkent@chromium.org>
Date: Tue Oct 30 07:02:29 2018

Add a UseCounter for parsing-but-no-painting -webkit-appearance values.

Also, add comments to ThemePainter::Paint() and
ThemePainter::PaintBorderOnly().

Bug:  892586 
Change-Id: Ie93e735418fccd2d068cced41b7bdc74ca782b5d
Reviewed-on: https://chromium-review.googlesource.com/c/1307019
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603813}
[modify] https://crrev.com/4b22f37270ca87b7d8f3c8c2a2eeabda9d10e6c5/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/4b22f37270ca87b7d8f3c8c2a2eeabda9d10e6c5/third_party/blink/renderer/core/paint/theme_painter.cc
[modify] https://crrev.com/4b22f37270ca87b7d8f3c8c2a2eeabda9d10e6c5/tools/metrics/histograms/enums.xml

The NextAction date has arrived: 2018-12-18

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c62f18e561018bf771367d30752cfbb004456686

commit c62f18e561018bf771367d30752cfbb004456686
Author: Kent Tamura <tkent@chromium.org>
Date: Tue Jan 15 12:16:19 2019

Fix UseCounter for -webkit-appearance computed style.

https://chromium-review.googlesource.com/c/1272759 intended to count
kGetComputedStyle*For*WebkitAppearance, but it actually counted
kGetComputedStyle**WebkitAppearance. This CL fixes this issue, and
renames kGetComputedStyleForWebkitAppearance to clarify what is counted.

Bug:  892586 
Change-Id: I3a374d397addf987ce363c01665ec2d789bdeb2f
Reviewed-on: https://chromium-review.googlesource.com/c/1405167
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622824}
[modify] https://crrev.com/c62f18e561018bf771367d30752cfbb004456686/third_party/blink/public/platform/web_feature.mojom
[modify] https://crrev.com/c62f18e561018bf771367d30752cfbb004456686/third_party/blink/renderer/core/css/css_computed_style_declaration.cc
[modify] https://crrev.com/c62f18e561018bf771367d30752cfbb004456686/tools/metrics/histograms/enums.xml

Is there data for this now?

From chromestatus.com I think the values that show up are, in order most used to least used:

none
button
textfield
menulist-button
checkbox
menulist
radio
push-button
textarea
listbox
caret (remove?)
inner-spin-button (remove?)
search-cancel (remove?)
search-field
slider-thumb-horizontal (remove?)
slider-horizontal
progress-bar
meter
slider-vertical
square-button (remove?)
slider-thumb-vertical (remove?)

Sorry I mistyped some values.

searchfield-cancel-button (remove?)
searchfield