Only alert accessibility when a notification's text changes

Bug: 867426
Change-Id: I7f220566f3e7a2b4ce7ef639d012f4323b762208
Reviewed-on: https://chromium-review.googlesource.com/1166231Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581474}

ui/message_center/views/message_popup_view.cc

@@ -65,11 +65,17 @@ MessagePopupView::MessagePopupView(PopupAlignmentDelegate* alignment_delegate,
 MessagePopupView::~MessagePopupView() = default;
 
 void MessagePopupView::UpdateContents(const Notification& notification) {
+  ui::AXNodeData old_data;
+  message_view_->GetAccessibleNodeData(&old_data);
   message_view_->UpdateWithNotification(notification);
   popup_collection_->NotifyPopupResized();
   if (notification.rich_notification_data()
           .should_make_spoken_feedback_for_popup_updates) {
-    NotifyAccessibilityEvent(ax::mojom::Event::kAlert, true);
+    ui::AXNodeData new_data;
+    message_view_->GetAccessibleNodeData(&new_data);
+    if (old_data.GetStringAttribute(ax::mojom::StringAttribute::kName) !=
+        new_data.GetStringAttribute(ax::mojom::StringAttribute::kName))
+      NotifyAccessibilityEvent(ax::mojom::Event::kAlert, true);
   }
 }