We should add a UseCounter first to evaluate a risk.

lunalu@, this seems like a small and contained change in a new area for you. I would suggest first preparing a CL that makes the test pass, then it'll be easier to judge what the risk involved is, and if we indeed need use counters first.

On second thought, this actually isn't IDL-related, was a bit quick on the trigger there.

Only the test cases which are related to "reversed", are failed.
Do we need to add usecounter for specific to this case ? Or can I make CL to pass the tests pass ?

#6,
We should count |start| IDL getter with |reversed| attribute and no |start| content attribute.
I don't recommend to make a bahavior change CL yet.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/846987251c417048faef232c657c83da59715eae

commit 846987251c417048faef232c657c83da59715eae
Author: shanmuga.m <shanmuga.m@samsung.com>
Date: Thu May 25 09:22:43 2017

Measure the usage of <ol>.start with |reversed| and no |start| attribute.

Add usecounter to measure the usage of <ol>.start which has
|reversed| attribute and no |start| content attribute.

BUG= 657972 

Review-Url: https://codereview.chromium.org/2902723006
Cr-Commit-Position: refs/heads/master@{#474614}

[modify] https://crrev.com/846987251c417048faef232c657c83da59715eae/third_party/WebKit/Source/core/frame/UseCounter.h
[modify] https://crrev.com/846987251c417048faef232c657c83da59715eae/third_party/WebKit/Source/core/html/HTMLOListElement.cpp
[modify] https://crrev.com/846987251c417048faef232c657c83da59715eae/third_party/WebKit/Source/core/html/HTMLOListElement.h
[modify] https://crrev.com/846987251c417048faef232c657c83da59715eae/tools/metrics/histograms/enums.xml

Wait for the UseCounter data.

The NextAction date has arrived: 2017-08-08

The counter: https://www.chromestatus.com/metrics/feature/timeline/popularity/2011

IMO, we may skip intent-to-ship process though a chromestatus.com entry is necessary.

chromestatus.com entry : https://www.chromestatus.com/feature/5763018952540160

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0

commit 8b676f1bd0267ee1a3f189a17567f8f7d10a15a0
Author: Shanmuga Pandi M <shanmuga.m@samsung.com>
Date: Tue Aug 22 09:41:17 2017

Update <ol>.start getter to default to 1.

Spec:
https://html.spec.whatwg.org/multipage/grouping-content.html#dom-ol-start

Bug:  657972 
Change-Id: I13da4bcb8d65d428b6b671fa1c44003c7901a164
Reviewed-on: https://chromium-review.googlesource.com/618215
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496261}
[delete] https://crrev.com/648a03cbb08c558d675d8530a124d52324506454/third_party/WebKit/LayoutTests/external/wpt/html/semantics/grouping-content/the-ol-element/grouping-ol-expected.txt
[delete] https://crrev.com/648a03cbb08c558d675d8530a124d52324506454/third_party/WebKit/LayoutTests/external/wpt/html/semantics/grouping-content/the-ol-element/ol.start-reflection-2-expected.txt
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/LayoutTests/fast/lists/ol-reversed-simple-expected.txt
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/LayoutTests/fast/lists/ol-reversed-simple-xhtml-expected.txt
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/Source/core/html/HTMLOListElement.cpp
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/Source/core/html/HTMLOListElement.h
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/Source/core/layout/LayoutCounter.cpp
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/Source/core/layout/LayoutListItem.cpp
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/third_party/WebKit/public/platform/web_feature.mojom
[modify] https://crrev.com/8b676f1bd0267ee1a3f189a17567f8f7d10a15a0/tools/metrics/histograms/enums.xml