Ensures that Web notifications are announced as soon as they appear

Switches to using an accessibility role of alert dialog which is more appropriate for a notification toast than a window role.
Alert dialogs are widgets that may contain interactive controls that need to be announced by a screen reader as soon as they appear.
Also, an alert event should be fired regardless to whether the notification has been updated or has been initiallly set.
R=aleventhal@chromium.org, dmazzoni@chromium.org, dewittj@chromium.org, peter@chromium.org

Tested: Manually with Jaws and NVDA screen readers on Windows
Change-Id: Ida3abe94b9dc32a5c95ce6b14c6fac11670348e3
Reviewed-on: https://chromium-review.googlesource.com/968672Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545510}

ui/message_center/views/message_popup_collection.cc

@@ -191,8 +191,14 @@ void MessagePopupCollection::UpdateWidgets() {
 
     ToastContentsView* toast = new ToastContentsView(
         notification.id(), alignment_delegate_, weak_factory_.GetWeakPtr());
+
+    const RichNotificationData& optional_fields =
+        notification.rich_notification_data();
+    bool a11y_feedback_for_updates =
+        optional_fields.should_make_spoken_feedback_for_popup_updates;
+
     // There will be no contents already since this is a new ToastContentsView.
-    toast->SetContents(view, /*a11y_feedback_for_updates=*/false);
+    toast->SetContents(view, a11y_feedback_for_updates);
     toasts_.push_back(toast);
 
     gfx::Size preferred_size = toast->GetPreferredSize();

ui/message_center/views/message_view.cc

@@ -6,6 +6,7 @@
 
 #include "base/feature_list.h"
 #include "base/strings/utf_string_conversions.h"
+#include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/models/simple_menu_model.h"
@@ -94,7 +95,11 @@ MessageView::~MessageView() {}
 
 void MessageView::UpdateWithNotification(const Notification& notification) {
   pinned_ = notification.pinned();
-  accessible_name_ = CreateAccessibleName(notification);
+  base::string16 new_accessible_name = CreateAccessibleName(notification);
+  if (new_accessible_name != accessible_name_) {
+    accessible_name_ = new_accessible_name;
+    NotifyAccessibilityEvent(ax::mojom::Event::kTextChanged, true);
+  }
   slide_out_controller_.set_enabled(!GetPinned());
 }
 

ui/message_center/views/toast_contents_view.cc

@@ -11,6 +11,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
+#include "ui/accessibility/ax_enums.mojom.h"
 #include "ui/accessibility/ax_node_data.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_targeter.h"
@@ -84,17 +85,11 @@ ToastContentsView::~ToastContentsView() {
 void ToastContentsView::SetContents(MessageView* view,
                                     bool a11y_feedback_for_updates) {
   message_view_ = view;
-  bool already_has_contents = child_count() > 0;
   RemoveAllChildViews(true);
   AddChildView(view);
   UpdatePreferredSize();
-
-  // If it has the contents already, this invocation means an update of the
-  // popup toast, and the new contents should be read through a11y feature.
-  // The notification type should be ALERT, otherwise the accessibility message
-  // won't be read for this view which returns ROLE_WINDOW.
-  if (already_has_contents && a11y_feedback_for_updates)
-    NotifyAccessibilityEvent(ax::mojom::Event::kAlert, false);
+  if (a11y_feedback_for_updates)
+    NotifyAccessibilityEvent(ax::mojom::Event::kAlert, true);
 }
 
 void ToastContentsView::UpdateContents(const Notification& notification,
@@ -104,7 +99,7 @@ void ToastContentsView::UpdateContents(const Notification& notification,
   message_view->UpdateWithNotification(notification);
   UpdatePreferredSize();
   if (a11y_feedback_for_updates)
-    NotifyAccessibilityEvent(ax::mojom::Event::kAlert, false);
+    NotifyAccessibilityEvent(ax::mojom::Event::kAlert, true);
 }
 
 void ToastContentsView::RevealWithAnimation(gfx::Point origin) {
@@ -316,7 +311,7 @@ void ToastContentsView::UpdatePreferredSize() {
 void ToastContentsView::GetAccessibleNodeData(ui::AXNodeData* node_data) {
   if (child_count() > 0)
     child_at(0)->GetAccessibleNodeData(node_data);
-  node_data->role = ax::mojom::Role::kWindow;
+  node_data->role = ax::mojom::Role::kAlertDialog;
 }
 
 const char* ToastContentsView::GetClassName() const {