Add deprecation warning banner to App Launcher on Mac.

ui/app_list/cocoa/app_list_view_controller.h

Index: ui/app_list/cocoa/app_list_view_controller.h
diff --git a/ui/app_list/cocoa/app_list_view_controller.h b/ui/app_list/cocoa/app_list_view_controller.h
index 3329dd15060cd71fa377570f4a81683238707c4a..6e8534e24b0566b15ee535b714267b2ce4ed3b6f 100644
--- a/ui/app_list/cocoa/app_list_view_controller.h
+++ b/ui/app_list/cocoa/app_list_view_controller.h
@@ -29,7 +29,8 @@ class AppListModelObserverBridge;
 APP_LIST_EXPORT
 @interface AppListViewController : NSViewController<AppsPaginationModelObserver,
                                                     AppsSearchBoxDelegate,
-                                                    AppsSearchResultsDelegate> {
+                                                    AppsSearchResultsDelegate,
+                                                    NSTextViewDelegate> {
  @private
   base::scoped_nsobject<AppsGridController> appsGridController_;
   base::scoped_nsobject<AppListPagerView> pagerControl_;
@@ -37,6 +38,10 @@ APP_LIST_EXPORT
   base::scoped_nsobject<AppsSearchResultsController>
       appsSearchResultsController_;
 
+  // If set, a message displayed above the app list grid.
+  base::scoped_nsobject<NSTextView> messageText_;
+  base::scoped_nsobject<NSScrollView> messageScrollView_;
+
   // Subview for drawing the background.
   base::scoped_nsobject<NSView> backgroundView_;