Use mojo SystemTray interfaces for both mash and classic ash

ash/mus/shell_delegate_mus.cc

Index: ash/mus/shell_delegate_mus.cc
diff --git a/ash/mus/shell_delegate_mus.cc b/ash/mus/shell_delegate_mus.cc
index 8f7bc3bc7ba4df65ac9a8ffb07c882e68ae2cb94..00968e7f469fff7ece20586e153a8da609361160 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -10,12 +10,12 @@
 #include "ash/common/media_delegate.h"
 #include "ash/common/palette_delegate.h"
 #include "ash/common/session/session_state_delegate.h"
+#include "ash/common/system/tray/default_system_tray_delegate.h"
 #include "ash/common/wm_shell.h"
 #include "ash/mus/accessibility_delegate_mus.h"
 #include "ash/mus/context_menu_mus.h"
 #include "ash/mus/new_window_delegate_mus.h"
 #include "ash/mus/shelf_delegate_mus.h"
-#include "ash/mus/system_tray_delegate_mus.h"
 #include "ash/mus/wallpaper_delegate_mus.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/string16.h"
@@ -170,7 +170,7 @@ ShelfDelegate* ShellDelegateMus::CreateShelfDelegate(ShelfModel* model) {
 }
 
 SystemTrayDelegate* ShellDelegateMus::CreateSystemTrayDelegate() {
-  return new SystemTrayDelegateMus(connector_);
+  return new DefaultSystemTrayDelegate;
 }
 
 std::unique_ptr<WallpaperDelegate> ShellDelegateMus::CreateWallpaperDelegate() {