aura: Uber tray should not show up on start screen in kiosk mode.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index d1a27098146c5b6ad793ced8cfa83ffe1304185e..ddaa406171af1a2fb7f07eec2c5746079dfbdd17 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -241,6 +241,8 @@ class DummySystemTrayDelegate : public SystemTrayDelegate {
  private:
 
   // Overridden from SystemTrayDelegate:
+  virtual bool GetTrayVisibilityOnStartup() OVERRIDE { return true; }
+
   virtual const std::string GetUserDisplayName() const OVERRIDE {
     return "Über tray Über tray Über tray Über tray";
   }
@@ -598,6 +600,8 @@ void Shell::Init() {
     tray_->AddTrayItem(new internal::TraySettings());
     tray_->AddTrayItem(tray_accessibility);
     tray_->AddTrayItem(tray_caps_lock);
+
+    tray_->SetVisible(tray_delegate_->GetTrayVisibilityOnStartup());
   }
   if (!status_widget_)
     status_widget_ = internal::CreateStatusArea(tray_.get());