Remove DisplayChangeObserver ash dependencies.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 8e0711e77eb9d79cc476c731d77ec3fac5eafeca..0234a6cfa660328bdd5494defb31578867d90e30 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -106,6 +106,7 @@ class ScreenPositionController;
 class SessionStateDelegate;
 class ShellDelegate;
 struct ShellInitParams;
+class ShutdownObserver;
 class StickyKeysController;
 class SystemGestureEventFilter;
 class SystemModalContainerEventFilter;
@@ -510,6 +511,9 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
   // Listens for output changes and updates the display manager.
   std::unique_ptr<DisplayChangeObserver> display_change_observer_;
 
+  // Listens for shutdown and updates DisplayConfigurator.
+  std::unique_ptr<ShutdownObserver> shutdown_observer_;
+
   // Implements content::ScreenOrientationController for ChromeOS
   std::unique_ptr<ScreenOrientationController> screen_orientation_controller_;
   std::unique_ptr<ScreenLayoutObserver> screen_layout_observer_;