Prepare SystemTray to support notifications

ash/system/tray_update.cc

Index: ash/system/tray_update.cc
diff --git a/ash/system/tray_update.cc b/ash/system/tray_update.cc
index 8d1399591a9bfd768662b64d8a1e63af33522f3c..f922dab649b9e68dba6b484d731b138033cfe45d 100644
--- a/ash/system/tray_update.cc
+++ b/ash/system/tray_update.cc
@@ -57,7 +57,8 @@ namespace ash {
 namespace internal {
 
 TrayUpdate::TrayUpdate()
-    : TrayImageItem(IDR_AURA_UBER_TRAY_UPDATE) {
+    : TrayImageItem(IDR_AURA_UBER_TRAY_UPDATE),
+      default_(NULL) {
 }
 
 TrayUpdate::~TrayUpdate() {}
@@ -69,12 +70,13 @@ bool TrayUpdate::GetInitialVisibility() {
 views::View* TrayUpdate::CreateDefaultView(user::LoginStatus status) {
   if (!Shell::GetInstance()->tray_delegate()->SystemShouldUpgrade())
     return NULL;
-  default_.reset(new UpdateView);
-  return default_.get();
+  DCHECK(default_ == NULL);
+  default_ = new UpdateView;
+  return default_;
 }
 
 void TrayUpdate::DestroyDefaultView() {
-  default_.reset();
+  default_ = NULL;
 }
 
 void TrayUpdate::OnUpdateRecommended() {