Add WebNotificationTray to the status area

ash/system/tray/system_tray_bubble.cc

Index: ash/system/tray/system_tray_bubble.cc
diff --git a/ash/system/tray/system_tray_bubble.cc b/ash/system/tray/system_tray_bubble.cc
index ff3430fc331539841d907354fb5a2fe954e43c43..690acf4bad13503b8d1b48f8518a3436ad644ab5 100644
--- a/ash/system/tray/system_tray_bubble.cc
+++ b/ash/system/tray/system_tray_bubble.cc
@@ -383,6 +383,19 @@ void SystemTrayBubble::Close() {
     bubble_widget_->Close();
 }
 
+void SystemTrayBubble::SetVisible(bool is_visible) {
+  if (!bubble_widget_)
+    return;
+  if (is_visible)
+    bubble_widget_->Show();
+  else
+    bubble_widget_->Hide();
+}
+
+bool SystemTrayBubble::IsVisible() {
+  return bubble_widget_ && bubble_widget_->IsVisible();
+}
+
 void SystemTrayBubble::CreateItemViews(user::LoginStatus login_status) {
   for (std::vector<ash::SystemTrayItem*>::iterator it = items_.begin();
        it != items_.end();