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 df7c2d5fdaedbfec9427320bbb942e1db96342c8..6888cc48e80f7708090ac04b7ef3126e00e7adc8 100644
--- a/ash/system/tray/system_tray_bubble.cc
+++ b/ash/system/tray/system_tray_bubble.cc
@@ -336,6 +336,7 @@ void SystemTrayBubble::InitView(const InitParams& init_params) {
 
 void SystemTrayBubble::BubbleViewDestroyed() {
   DestroyItemViews();
+  bubble_view_ = NULL;
 }
 
 gfx::Rect SystemTrayBubble::GetAnchorRect() const {
@@ -422,6 +423,19 @@ 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();