MD system tray: Avoid adding separator as the first item of Bluetooth device list.

ash/common/system/chromeos/bluetooth/tray_bluetooth.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/system/chromeos/bluetooth/tray_bluetooth.h"
 
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/system/tray/fixed_sized_scroll_view.h"
 #include "ash/common/system/tray/hover_highlight_view.h"
@@ skipping 313 matching lines @@
     }
 
     AppendSameTypeDevicesToScrollList(connected_devices_, true, true,
                                       bluetooth_enabled);
     AppendSameTypeDevicesToScrollList(connecting_devices_, true, false,
                                       bluetooth_enabled);
     AppendSameTypeDevicesToScrollList(paired_not_connected_devices_, false,
                                       false, bluetooth_enabled);
     if (discovered_not_paired_devices_.size() > 0) {
       if (UseMd()) {
-        scroll_content()->AddChildView(
-            TrayPopupUtils::CreateListItemSeparator(false));
+        if (scroll_content()->has_children()) {
+          scroll_content()->AddChildView(
+              TrayPopupUtils::CreateListItemSeparator(false));
+        }
       } else {
         AddScrollSeparator();
       }
     }
     AppendSameTypeDevicesToScrollList(discovered_not_paired_devices_, false,
                                       false, bluetooth_enabled);
 
     // Show user Bluetooth state if there is no bluetooth devices in list.
     if (device_map_.size() == 0) {
       if (bluetooth_available && bluetooth_enabled) {
@@ skipping 415 matching lines @@
     detailed_->Update();
 }
 
 void TrayBluetooth::OnBluetoothDiscoveringChanged() {
   if (!detailed_)
     return;
   detailed_->Update();
 }
 
 }  // namespace ash