Given the compat analysis already done at https://github.com/whatwg/dom/issues/211, I suspect this will be really easy (but does still need an intent - http://www.chromium.org/blink#TOC-Policy-for-shipping-and-removing-web-platform-API-features).

Given the obscurity I probably wouldn't bother with any outreach (no chromestatus entry), but we should probably still have a one milestone deprecation warning period just in case.  

Making the EventCancelBubbleWasChangedToFalse counter into a Deprecation will be trivial: https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/events/Event.cpp?sq=package:chromium&dr=CSs&rcl=1482265342&l=343.  Then a milestone later we should probably replace that counter with a simple console warning saying the method is a no-op and early out.

This is probably a good chance for someone to do their first blink "intent to deprecate and remove" if someone is interested.

I am interested in doing it, assign to myself.

Feature freeze of M57 is Jan 06 2017, does that mean in "Intent to deprecate" we should indicate we are going to deprecate it in M58?

If you send out an Intent to Deprecate and Remove, deprecating in M58 and making the change in M59 (or later, could make it M61) makes sense. Not so much because of the feature freeze date but just because there might not be time to get 3xLGTM before the branch point. (Merging back to M57 is possible but if there's no hurry not necessary.)

Issue 657651 has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b461901d4922144f8cd88810a60e23a3a5d08e4c

commit b461901d4922144f8cd88810a60e23a3a5d08e4c
Author: lpy <lpy@chromium.org>
Date: Wed Jan 25 21:13:00 2017

Remove setting cancelBubble to false.

According to spec https://dom.spec.whatwg.org/#dom-event-cancelbubble, setting
cancelBubble to true is considered as an alias to stopPropagation(), setting
cancelBubble to false is a no-op. Detail discussion is on
https://github.com/whatwg/dom/issues/211.

BUG= 675549 

Review-Url: https://codereview.chromium.org/2641953006
Cr-Commit-Position: refs/heads/master@{#446118}

[delete] https://crrev.com/76a10b17535c0456f042817a69fa036f226b26a3/third_party/WebKit/LayoutTests/external/wpt/dom/events/Event-cancelBubble-expected.txt
[delete] https://crrev.com/76a10b17535c0456f042817a69fa036f226b26a3/third_party/WebKit/LayoutTests/external/wpt/dom/events/Event-dispatch-bubble-canceled-expected.txt
[delete] https://crrev.com/76a10b17535c0456f042817a69fa036f226b26a3/third_party/WebKit/LayoutTests/external/wpt/dom/events/Event-dispatch-multiple-cancelBubble-expected.txt
[delete] https://crrev.com/76a10b17535c0456f042817a69fa036f226b26a3/third_party/WebKit/LayoutTests/external/wpt/dom/events/Event-propagation-expected.txt
[modify] https://crrev.com/b461901d4922144f8cd88810a60e23a3a5d08e4c/third_party/WebKit/Source/core/events/Event.cpp
[modify] https://crrev.com/b461901d4922144f8cd88810a60e23a3a5d08e4c/third_party/WebKit/Source/core/events/Event.h
[modify] https://crrev.com/b461901d4922144f8cd88810a60e23a3a5d08e4c/third_party/WebKit/Source/core/events/EventDispatcher.cpp
[modify] https://crrev.com/b461901d4922144f8cd88810a60e23a3a5d08e4c/third_party/WebKit/Source/core/frame/UseCounter.h
[modify] https://crrev.com/b461901d4922144f8cd88810a60e23a3a5d08e4c/third_party/WebKit/Source/modules/indexeddb/IDBEventDispatcher.cpp
[modify] https://crrev.com/b461901d4922144f8cd88810a60e23a3a5d08e4c/tools/metrics/histograms/histograms.xml

Shall I just close this bug as fixed?

I think so. I added the M-58 label, do you look at any other information, jmedley@?

I've got it on my list. Do you have stats on how many pages this could break? I'm not convinced it can do without a Chrome Status entry.

The relevant counter was https://www.chromestatus.com/metrics/feature/timeline/popularity/1350, so not exactly zero but rounding to zero.

Remove Blink>DOM>Events