Thanks! Fix out for review: https://codereview.chromium.org/1809573003/

The only thing I did differently is that I think Chrome should actually report an action and handle accDoDefaultAction when an element has a click listener. I think it's more robust for us to simulate the click internally where we know we can. It was a bug that we weren't handling div with an onclick attribute.

In the case of calling accDoDefaultAction on an element without a click listener I agree completely and I made it return DISP_E_MEMBERNOTFOUND.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/30fc95f3dd93562d7be852205c49bd49e793d84c

commit 30fc95f3dd93562d7be852205c49bd49e793d84c
Author: dmazzoni <dmazzoni@chromium.org>
Date: Fri Mar 18 08:28:41 2016

Fix support for accessible action verbs and performing the default action.

Accessible objects support a "default action" if something happens when
you click on them. On some platforms we return a localized string like
"press" or "uncheck" indicating what action will occur. This change fixes
a few cases that weren't correct:

1. A few objects had actions but no verb - fix this by adding a verb for
   pop-up buttons ("open") and a default verb when nothing else applies
   ("click").

2. Ensure we always return an action verb when an object has a default
   action, and never otherwise.

3. Fix detection of click event listeners - we were using an API that
   only returned some; use the right API to get all click-and-mouse-related
   event listeners, but exclude the HTML BODY element because lots of
   pages have click listeners there and they're rarely what we want.

4. The Windows API accDoDefaultAction should return an error if called on
   an object with no default action.

BUG= 595222 

Review URL: https://codereview.chromium.org/1809573003

Cr-Commit-Position: refs/heads/master@{#381911}

[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/content/app/strings/content_strings.grd
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/content/browser/accessibility/browser_accessibility_win.cc
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/content/browser/accessibility/dump_accessibility_tree_browsertest.cc
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/content/child/blink_platform_impl.cc
[add] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/content/test/data/accessibility/html/action-verbs-expected-blink.txt
[add] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/content/test/data/accessibility/html/action-verbs.html
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/LayoutTests/accessibility/press-works-on-control-types-expected.txt
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/LayoutTests/accessibility/press-works-on-control-types.html
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/Source/modules/accessibility/AXLayoutObject.h
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/Source/modules/accessibility/AXNodeObject.cpp
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/Source/modules/accessibility/AXObject.cpp
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/Source/modules/accessibility/AXObject.h
[modify] https://crrev.com/30fc95f3dd93562d7be852205c49bd49e793d84c/third_party/WebKit/public/platform/WebLocalizedString.h

"3. Fix detection of click event listeners - we were using an API that
   only returned some; use the right API to get all click-and-mouse-related
   event listeners, but exclude the HTML BODY element because lots of
   pages have click listeners there and they're rarely what we want."

Chrome's accessibility tree indicates that all hypertext elements that are contained w/in a parent element w/ at least one "click-and-mouse-related" event listener now have the "click" default action. THIS causes some accessibility related assertive technologies (JAWS, NVDA, ...) to misinterpret all hypertext as "clickable".

This change in behavior goes against how some JavaScript libraries's (jQuery) event delegation works when capturing (at a higher level in the DOM) events that occur on any element w/in the document (Not ONLY the HTML BODY). 

This assumes one can only:
1. bind event handlers directly to the objects where the event happens
2. bind all delegated event handlers to the document object

This is not true especially when the objects you are capturing events on are dynamically created/removed and you still want to capture events on them without having to explicitly rebind event handlers every time you create a new one.

@rlamtabbet thanks for the report, and the  issue 662254 .
Probably it's better to continue discussion there?
(I'm just adding the reference to it so people can follow)

I wouldn't mind changing what Chrome exposes but we need to figure out a way to tell users whether something is clickable. The assistive software you mention announces "clickable" for a good reason. Many web apps have widgets that don't use the correct ARIA or HTML attributes to indicate their role. So, a blind user has no way of knowing what they can activate or not. Many times the context, i.e. what the page says, is not enough. You need to know exactly where and what to click.
Excluding click handlers on the body element was just a heuristic.