Remove DisplayChangeObserver ash dependencies.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 313a75dc618906dd83c4589748bb5aa08620ca79..809728020a91076916da5a45cbc15b1970332553 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -111,6 +111,7 @@ class ScreenPositionController;
 class SessionStateDelegate;
 class ShellDelegate;
 struct ShellInitParams;
+class ShutdownObserver;
 class SlowAnimationEventFilter;
 class StatusAreaWidget;
 class StickyKeysController;
@@ -518,6 +519,9 @@ 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_;