mash: Have chrome set itself as the app list presenter.

ui/app_list/presenter/app_list_presenter.mojom

Index: ui/app_list/presenter/app_list_presenter.mojom
diff --git a/ui/app_list/presenter/app_list_presenter.mojom b/ui/app_list/presenter/app_list_presenter.mojom
index 3ffa45af8f7f9b6eae8ed33a0fcfae5ee5f55ca5..8522ca5805f0992728b2f2cf1163fca4061f30b1 100644
--- a/ui/app_list/presenter/app_list_presenter.mojom
+++ b/ui/app_list/presenter/app_list_presenter.mojom
@@ -6,6 +6,17 @@ module app_list.mojom;
 
 import "services/ui/public/interfaces/window_manager_constants.mojom";
 
+// TODO(msw): Rename this file to app_list.mojom; move to ash?
+// TODO(msw): Ash should implement the app list and presenter; chrome should
+//            just push data about its apps into the app list interface.
+
+// Implemented by ash. Used by chrome to set the presenter interface.
+interface AppList {
+  // Set the app list presenter interface, to let ash trigger Chrome's app list.
+  SetAppListPresenter(AppListPresenter presenter);
+};
+
+// Implemented by chrome. Used by ash to actually show and dismiss the app list.
 interface AppListPresenter {
   // Show the app list on the specified display.
   Show(int64 display_id);