https://bugs.webkit.org/show_bug.cgi?id=100275

Reviewed by Chris Fleizach.

Source/WebCore:

Test: accessibility/children-changed-sends-notification.html

Emit children-changed::add and children-changed::remove whenever
an object has been added/removed to the accessibility hierarchy,
that is, when a new AtkObject is being attached/detached.

* accessibility/AXObjectCache.h:
(WebCore::AXObjectCache::detachWrapper): Added a new parameter and
updated all the prototypes in different ports.
* accessibility/AXObjectCache.cpp:
(WebCore::AXObjectCache::~AXObjectCache): Call detachWrapper()
specifying that we do it because the cache is being destroyed.
(WebCore::AXObjectCache::remove): Call detachWrapper() specifying
that we do it because an accessible element is being destroyed.

* accessibility/atk/AXObjectCacheAtk.cpp:
(WebCore::AXObjectCache::detachWrapper): Emit the children-changed
signal when needed. We rely on the cached reference to the parent
AtkObject (using the implementation of atk_object_get_parent from
the AtkObject class) to find the right object to emit the signal
from here, since the accessibility hierarchy from WebCore will no
longer be accessible at this point.
(WebCore::AXObjectCache::attachWrapper): Emit the children-change
signal from here unless we are in the middle of a layout update,
trying to provide as much information (e.g. the offset) as possible.
(WebCore::AXObjectCache::postPlatformNotification): Make sure we
update (touch) the subtree under an accessibility object whenever
we receive AXChildrenChanded from WebCore, to ensure that those
objects will also be visible rightaway to ATs, and that those get
properly notified of the event at that very same moment.

* accessibility/ios/AXObjectCacheIOS.mm:
(WebCore::AXObjectCache::detachWrapper): Updated function signature.
* accessibility/mac/AXObjectCacheMac.mm:
(WebCore::AXObjectCache::detachWrapper): Ditto.
* accessibility/win/AXObjectCacheWin.cpp:
(WebCore::AXObjectCache::detachWrapper): Ditto.

* accessibility/AccessibilityObject.cpp:
(WebCore::AccessibilityObject::children): Add the option ot
request the AccessibilityChildrenVector without updating it if
needed, to avoid maybe recreating the child subtree when trying to
get the offset of a newly attached element from attachWrapper.
* accessibility/AccessibilityObject.h:

Tools:

Update DRT and WebKitTestRunner to handle the children-changed
signal properly, considering the detail and optional parameters.

* DumpRenderTree/atk/AccessibilityCallbacksAtk.cpp: Updated.
(axObjectEventListener):
* WebKitTestRunner/InjectedBundle/atk/AccessibilityNotificationHandlerAtk.cpp: Updated.

LayoutTests:

Add new test to chack that children-changed signals are properly
emitted when adding/removing elements in the accessibility hierarchy.

* accessibility/children-changed-sends-notification-expected.txt: Added.
* accessibility/children-changed-sends-notification.html: Added.

Update test to filter out unrelated non-loading events.
* accessibility/loading-iframe-sends-notification.html: Updated.

Skip the test on the Mac as it does not expose these kind of
notifications when children are being added or removed.
* platform/mac/TestExpectations: Skip newly added test.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160903 268f45cc-cd09-0410-ab3c-d52691b4dbfc