Moves maintaining ShellObservers back to Shell

ash/display/shutdown_observer_chromeos.cc

Index: ash/display/shutdown_observer_chromeos.cc
diff --git a/ash/display/shutdown_observer_chromeos.cc b/ash/display/shutdown_observer_chromeos.cc
index a29830b534fd1c341c729e34607c994651e569c8..145d2f545a5264658e97338c64e30cf9625b71b6 100644
--- a/ash/display/shutdown_observer_chromeos.cc
+++ b/ash/display/shutdown_observer_chromeos.cc
@@ -4,7 +4,7 @@
 
 #include "ash/display/shutdown_observer_chromeos.h"
 
-#include "ash/common/wm_shell.h"
+#include "ash/shell.h"
 #include "ui/display/manager/chromeos/display_configurator.h"
 
 namespace ash {
@@ -12,11 +12,11 @@ namespace ash {
 ShutdownObserver::ShutdownObserver(
     display::DisplayConfigurator* display_configurator)
     : display_configurator_(display_configurator) {
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 ShutdownObserver::~ShutdownObserver() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void ShutdownObserver::OnAppTerminating() {