Use mojo SystemTray interfaces for both mash and classic ash

ash/common/system/tray/system_tray.cc

Index: ash/common/system/tray/system_tray.cc
diff --git a/ash/common/system/tray/system_tray.cc b/ash/common/system/tray/system_tray.cc
index 06c41736db80c751fe9b728fd7b3d5ee54f8ad6a..d8930080cb33bc1b0f3e4182a686b82349171fa7 100644
--- a/ash/common/system/tray/system_tray.cc
+++ b/ash/common/system/tray/system_tray.cc
@@ -13,6 +13,7 @@
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/system/cast/tray_cast.h"
 #include "ash/common/system/date/tray_date.h"
+#include "ash/common/system/tray/system_tray_controller.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "ash/common/system/tray/system_tray_item.h"
 #include "ash/common/system/tray/tray_bubble_wrapper.h"
@@ -667,7 +668,7 @@ void SystemTray::UpdateWebNotifications() {
 base::string16 SystemTray::GetAccessibleTimeString(
     const base::Time& now) const {
   base::HourClockType hour_type =
-      WmShell::Get()->system_tray_delegate()->GetHourClockType();
+      WmShell::Get()->system_tray_controller()->hour_clock_type();
   return base::TimeFormatTimeOfDayWithHourClockType(now, hour_type,
                                                     base::kKeepAmPm);
 }