Add the supporting code for the cast system tray integration

ash/system/tray/system_tray_delegate.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/system/tray/system_tray_delegate.h"
 
 namespace ash {
 
 NetworkIconInfo::NetworkIconInfo()
     : connecting(false),
@@ skipping 205 matching lines @@
   return false;
 }
 
 bool SystemTrayDelegate::GetBluetoothDiscovering() {
   return false;
 }
 
 void SystemTrayDelegate::ChangeProxySettings() {
 }
 
+CastConfigDelegate* SystemTrayDelegate::GetCastConfigDelegate() const {
+  return nullptr;
+}
+
 NetworkingConfigDelegate* SystemTrayDelegate::GetNetworkingConfigDelegate()
     const {
   return nullptr;
 }
 
 VolumeControlDelegate* SystemTrayDelegate::GetVolumeControlDelegate() const {
   return nullptr;
 }
 
 void SystemTrayDelegate::SetVolumeControlDelegate(
@@ skipping 44 matching lines @@
 
 void SystemTrayDelegate::ShouldRebootOnShutdown(
     const RebootOnShutdownCallback& callback) {
 }
 
 VPNDelegate* SystemTrayDelegate::GetVPNDelegate() const {
   return nullptr;
 }
 
 }  // namespace ash