Add UI for cast system tray integration

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index 34bb447c23113dc1ba183b0f38b5dd3bda79a930..baca0ad2c61e803374d722b02be2f85c958f4867 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -11,6 +11,7 @@
 #include "ash/shell_window_ids.h"
 #include "ash/system/audio/tray_audio.h"
 #include "ash/system/bluetooth/tray_bluetooth.h"
+#include "ash/system/cast/tray_cast.h"
 #include "ash/system/date/tray_date.h"
 #include "ash/system/status_area_widget.h"
 #include "ash/system/tray/system_tray_delegate.h"
@@ -181,6 +182,7 @@ void SystemTray::CreateItems(SystemTrayDelegate* delegate) {
   AddTrayItem(new TrayVPN(this));
   AddTrayItem(new TraySms(this));
   AddTrayItem(new TrayBluetooth(this));
+  AddTrayItem(new TrayCast(this));
   AddTrayItem(new TrayDisplay(this));
   screen_capture_tray_item_ = new ScreenCaptureTrayItem(this);
   AddTrayItem(screen_capture_tray_item_);
@@ -203,6 +205,7 @@ void SystemTray::CreateItems(SystemTrayDelegate* delegate) {
 #elif defined(OS_LINUX)
   AddTrayItem(tray_accessibility_);
   AddTrayItem(new TrayBluetooth(this));
+  AddTrayItem(new TrayCast(this));
   AddTrayItem(new TrayUpdate(this));
   AddTrayItem(tray_date_);
 #endif