Fix issue where iframe content wasn't included in the accessibility tree

Fix issue where iframe content wasn't included in the accessibility tree
https://bugs.webkit.org/show_bug.cgi?id=117456

Reviewed by Chris Fleizach.

Merge - https://chromium.googlesource.com/chromium/blink/+/af4e73e2bfb32fce56854ef0dab33077c7fa6bff

Have RenderWidget notify the accessibility object when its widget changes, otherwise the
AccessibilityRenderObject for the iframe might have a stale reference to the previous widget. (This
would not crash, it would just result in an empty subtree until some other event triggered it to
update.)

This allows us to re-enable this test, that was previously failing flakily or being skipped because
of this bug: loading-iframe-updates-axtree.html

* Source/WebCore/rendering/RenderWidget.cpp:
(WebCore::RenderWidget::setWidget): Update to add stale condition
* LayoutTests/platform/win/TestExpectations: Remove Skipped Test "loading-iframe-updates-axtree.html"
* LayoutTests/platform/wincairo-wk1/TestExpectations: Remove Skipped Test "loading-iframe-updates-axtree.html"
* LayoutTests/platform/wk2/TestExpectations: Remove Skipped Test "loading-iframe-updates-axtree.html"
* LayoutTests/platform/mac/accessibility/loading-iframe-updates-axtree-expected.txt: Add Platform Specific Test Expectations
* LayoutTests/accessibility/loading-iframe-updates-axtree-expected.txt: Update Test Expectations

Canonical link: https://commits.webkit.org/255407@main

LayoutTests/accessibility/loading-iframe-updates-axtree-expected.txt

@@ -11,9 +11,10 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 
 
 iframe.isEqual(newIframe): true
-scrollarea.isEqual(newScrollarea): false
+scrollarea.isEqual(newScrollarea): true
 subwebarea.isEqual(newSubwebarea): false
 PASS newSubwebarea.childrenCount > 0 is true
+PASS successfullyParsed is true
 
 TEST COMPLETE
 

LayoutTests/platform/mac/accessibility/loading-iframe-updates-axtree-expected.txt

@@ -0,0 +1,20 @@
+Before
+
+
+After
+
+End of test
+
+This tests that if an iframe loads new content after its accessibility object has already been accessed, the iframe accessibility object's descendants are the new scroll area and web area, not the old deleted ones.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+iframe.isEqual(newIframe): true
+scrollarea.isEqual(newScrollarea): false
+subwebarea.isEqual(newSubwebarea): false
+PASS newSubwebarea.childrenCount > 0 is true
+PASS successfullyParsed is true
+
+TEST COMPLETE
+

LayoutTests/platform/win/TestExpectations

@@ -1805,7 +1805,6 @@ webkit.org/b/193371 accessibility/set-selected-editable.html [ Skip ]
 webkit.org/b/140798 accessibility/aria-expanded-supported-roles.html [ Skip ]
 
 # The following timeouts are caused by the same problem: [ Failure ]
-webkit.org/b/126066 accessibility/loading-iframe-updates-axtree.html [ Skip ]
 webkit.org/b/140798 accessibility/aria-hidden-false-works-in-subtrees.html [ Skip ]
 
 # The following fail because of missing numerical output support.

LayoutTests/platform/wincairo-wk1/TestExpectations

@@ -98,8 +98,6 @@ webkit.org/b/140798 accessibility/textarea-insertion-point-line-number.html [ Fa
 webkit.org/b/140798 accessibility/th-as-title-ui.html [ Failure ]
 webkit.org/b/140798 accessibility/title-ui-element-correctness.html [ Failure ]
 
-webkit.org/b/126066 accessibility/loading-iframe-updates-axtree.html [ Failure ]
-
 webkit.org/b/140798 [ Debug ] accessibility/aria-hidden-false-works-in-subtrees.html [ Skip ]
 
 # The following fail because of missing numerical output support.

LayoutTests/platform/wk2/TestExpectations

@@ -45,9 +45,6 @@
 webkit.org/b/156612 http/tests/security/contentSecurityPolicy/embed-redirect-blocked3.html [ Failure ]
 webkit.org/b/156612 http/tests/security/contentSecurityPolicy/object-redirect-blocked3.html [ Failure ]
 
-# AX tests that require hit testing do not work in WK2.
-webkit.org/b/71298 accessibility/loading-iframe-updates-axtree.html
-
 # This test has been skipped for a long time. Temporarily marking as flaky to see what bots think.
 webkit.org/b/48354 compositing/iframes/iframe-src-change.html [ Pass Failure ]
 

Source/WebCore/rendering/RenderWidget.cpp

@@ -207,6 +207,9 @@ void RenderWidget::setWidget(RefPtr<Widget>&& widget)
         }
         moveWidgetToParentSoon(*m_widget, &view().frameView());
     }
+
+    if (auto* cache = document().existingAXObjectCache())
+        cache->childrenChanged(this);
 }
 
 void RenderWidget::layout()