Update the accessibility tree when a modal dialog is opened/closed.

Source/core/accessibility/AXObjectCache.cpp

Index: Source/core/accessibility/AXObjectCache.cpp
diff --git a/Source/core/accessibility/AXObjectCache.cpp b/Source/core/accessibility/AXObjectCache.cpp
index 950b465e1631fe9d9d3ef2f458929255275033e8..970156ca2da6dae5b1d5e31ab43cc98680a87656 100644
--- a/Source/core/accessibility/AXObjectCache.cpp
+++ b/Source/core/accessibility/AXObjectCache.cpp
@@ -650,6 +650,22 @@ void AXObjectCache::updateCacheAfterNodeIsAttached(Node* node)
     get(node);
 }
 
+static void inertSubtreesChanged(AXObject* object)
+{
+    if (object->notifyIfIgnoredValueChanged())
+        return;
+    AXObject::AccessibilityChildrenVector children = object->children();
+    size_t count = children.size();
+    for (size_t i = 0; i < count; ++i)
+        inertSubtreesChanged(children[i].get());
+}
+
+void AXObjectCache::handleInertSubtreesChanged()
+{
+    m_computedObjectAttributeCache->clear();
+    inertSubtreesChanged(rootObject());
+}
+
 void AXObjectCache::childrenChanged(Node* node)
 {
     childrenChanged(get(node));