Fire notification when virtual AccessibleNode attribute changes.

Previously firing a notification only worked when an AccessibleNode
had an element. Add a quick fix to ensure it works even when it
doesn't.

Bug: 761901
Change-Id: I0ec6723e748947d94f1207f72f38ec94f0f6b335
Reviewed-on: https://chromium-review.googlesource.com/962862
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573404}

third_party/blink/renderer/core/dom/accessible_node.cc

@@ -644,9 +644,7 @@ AtomicString AccessibleNode::current() const {
 
 void AccessibleNode::setCurrent(const AtomicString& current) {
   SetStringProperty(AOMStringProperty::kCurrent, current);
-
-  if (AXObjectCache* cache = GetAXObjectCache())
-    cache->HandleAttributeChanged(aria_currentAttr, element_);
+  NotifyAttributeChanged(aria_currentAttr);
 }
 
 AccessibleNodeList* AccessibleNode::describedBy() {
@@ -1173,8 +1171,12 @@ void AccessibleNode::NotifyAttributeChanged(
     const blink::QualifiedName& attribute) {
   // TODO(dmazzoni): Make a cleaner API for this rather than pretending
   // the DOM attribute changed.
-  if (AXObjectCache* cache = GetAXObjectCache())
-    cache->HandleAttributeChanged(attribute, element_);
+  if (AXObjectCache* cache = GetAXObjectCache()) {
+    if (element_)
+      cache->HandleAttributeChanged(attribute, element_);
+    else
+      cache->HandleAttributeChanged(attribute, this);
+  }
 }
 
 AXObjectCache* AccessibleNode::GetAXObjectCache() {

third_party/blink/renderer/core/dom/ax_object_cache.h

@@ -103,6 +103,10 @@ class CORE_EXPORT AXObjectCache
   virtual void HandleLayoutComplete(Document*) = 0;
   virtual void HandleClicked(Node*) = 0;
 
+  // Changes to virtual Accessibility Object Model nodes.
+  virtual void HandleAttributeChanged(const QualifiedName& attr_name,
+                                      AccessibleNode*) = 0;
+
   virtual void SetCanvasObjectBounds(HTMLCanvasElement*,
                                      Element*,
                                      const LayoutRect&) = 0;

third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.cc

@@ -869,6 +869,14 @@ void AXObjectCacheImpl::HandleClicked(Node* node) {
     PostNotification(obj, kAXClicked);
 }
 
+void AXObjectCacheImpl::HandleAttributeChanged(
+    const QualifiedName& attr_name,
+    AccessibleNode* accessible_node) {
+  modification_count_++;
+  if (AXObject* obj = Get(accessible_node))
+    PostNotification(obj, kAXAriaAttributeChanged);
+}
+
 void AXObjectCacheImpl::HandleAriaExpandedChange(Node* node) {
   if (AXObject* obj = GetOrCreate(node))
     obj->HandleAriaExpandedChanged();

third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.h

@@ -150,6 +150,8 @@ class MODULES_EXPORT AXObjectCacheImpl
   void HandleLoadComplete(Document*) override;
   void HandleLayoutComplete(Document*) override;
   void HandleClicked(Node*) override;
+  void HandleAttributeChanged(const QualifiedName& attr_name,
+                              AccessibleNode*) override;
 
   void SetCanvasObjectBounds(HTMLCanvasElement*,
                              Element*,

third_party/blink/renderer/modules/accessibility/ax_virtual_object.cc

@@ -33,6 +33,11 @@ void AXVirtualObject::AddChildren() {
     children_.push_back(AXObjectCache().GetOrCreate(child));
 }
 
+void AXVirtualObject::ChildrenChanged() {
+  ClearChildren();
+  AXObjectCache().PostNotification(this, AXObjectCacheImpl::kAXChildrenChanged);
+}
+
 const AtomicString& AXVirtualObject::GetAOMPropertyOrARIAAttribute(
     AOMStringProperty property) const {
   if (!accessible_node_)

third_party/blink/renderer/modules/accessibility/ax_virtual_object.h

@@ -24,6 +24,7 @@ class MODULES_EXPORT AXVirtualObject : public AXObject {
   AXObject* ComputeParent() const override { return parent_; }
   bool IsVirtualObject() const override { return true; }
   void AddChildren() override;
+  void ChildrenChanged() override;
   const AtomicString& GetAOMPropertyOrARIAAttribute(
       AOMStringProperty) const override;
   bool HasAOMPropertyOrARIAAttribute(AOMBooleanProperty,