chromeos: Move device shutdown handling out of chrome into ash

ash/common/system/tray/system_tray_delegate.cc

Index: ash/common/system/tray/system_tray_delegate.cc
diff --git a/ash/common/system/tray/system_tray_delegate.cc b/ash/common/system/tray/system_tray_delegate.cc
index d30bc104db836b42a8103762087f4832f7848048..929c031ee679ab2e5c040a002026cfa4b37dd7df 100644
--- a/ash/common/system/tray/system_tray_delegate.cc
+++ b/ash/common/system/tray/system_tray_delegate.cc
@@ -158,15 +158,6 @@ void SystemTrayDelegate::AddCustodianInfoTrayObserver(
 void SystemTrayDelegate::RemoveCustodianInfoTrayObserver(
     CustodianInfoTrayObserver* observer) {}
 
-void SystemTrayDelegate::AddShutdownPolicyObserver(
-    ShutdownPolicyObserver* observer) {}
-
-void SystemTrayDelegate::RemoveShutdownPolicyObserver(
-    ShutdownPolicyObserver* observer) {}
-
-void SystemTrayDelegate::ShouldRebootOnShutdown(
-    const RebootOnShutdownCallback& callback) {}
-
 VPNDelegate* SystemTrayDelegate::GetVPNDelegate() const {
   return nullptr;
 }