Adds AppListDelegate to AppList that is notified on visibility changes

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 66b0322f5d32419311bf95ca44095d9ea7224dae..f1cd86b90381e5930bffce14c58d7df551f30f66 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -72,6 +72,7 @@ class WindowModalityController;
 namespace ash {
 
 class AcceleratorControllerDelegateAura;
+class AppListDelegateImpl;
 class AshNativeCursorManager;
 class AutoclickController;
 class BluetoothNotificationController;
@@ -550,6 +551,8 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
 
   std::unique_ptr<ImmersiveHandlerFactoryAsh> immersive_handler_factory_;
 
+  std::unique_ptr<AppListDelegateImpl> app_list_delegate_impl_;
+
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };