https://bugs.webkit.org/show_bug.cgi?id=126993

Reviewed by Mario Sanchez Prada.

Source/WebCore: 

To monitor for menu open notifications, we need to know which children are added to
the render tree, so the childrenChanged() method has been updated to allow for that.
Once we know the new child, we can then check what kind of role it has.

I also found a flakiness issue with DRT where posting a notification back to DRT
would sometimes cause a new notification to be queued, which would then be lost when the
queue was cleared. This was fixed by copying the notifications to post before iterating them.

Test: platform/mac/accessibility/aria-menu-open-notification.html

* accessibility/AXObjectCache.cpp:
(WebCore::AXObjectCache::checkForOpenMenu):
(WebCore::AXObjectCache::childrenChanged):
(WebCore::AXObjectCache::notificationPostTimerFired):
* accessibility/AXObjectCache.h:
(WebCore::AXObjectCache::childrenChanged):
* accessibility/AccessibilityNodeObject.h:
* accessibility/mac/AXObjectCacheMac.mm:
(WebCore::AXObjectCache::postPlatformNotification):
* rendering/RenderElement.cpp:
(WebCore::RenderElement::insertChildInternal):
(WebCore::RenderElement::styleWillChange):

LayoutTests: 

* platform/mac/accessibility/aria-menu-open-notification-expected.txt: Added.
* platform/mac/accessibility/aria-menu-open-notification.html: Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162132 268f45cc-cd09-0410-ab3c-d52691b4dbfc