Change message view accessiblity node role

Changing the node role to kGenericContainer so that accessiblity
focus moves through all child elements.

Bug: 1009705
Change-Id: I7193521707d747fcc5e7a4b1b1c45da6b569a64a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1947191Reviewed-by: David Tseng <dtseng@chromium.org>
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721155}

ui/message_center/views/message_view.cc

@@ -209,7 +209,7 @@ void MessageView::OnContainerAnimationEnded() {
 }
 
 void MessageView::GetAccessibleNodeData(ui::AXNodeData* node_data) {
-  node_data->role = ax::mojom::Role::kButton;
+  node_data->role = ax::mojom::Role::kGenericContainer;
   node_data->AddStringAttribute(
       ax::mojom::StringAttribute::kRoleDescription,
       l10n_util::GetStringUTF8(IDS_MESSAGE_NOTIFICATION_ACCESSIBLE_NAME));