WIP: Eliminate event.target() usage from TrayEventFilter

ash/mus/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//mojo/public/mojo_application.gni")
 import("//mojo/public/mojo_application_manifest.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//tools/grit/repack.gni")
 
 source_set("lib") {
   sources = [
     "app_list_presenter_mus.cc",
     "app_list_presenter_mus.h",
+    "container_delegate_mus.cc",
+    "container_delegate_mus.h",
     "context_menu_mus.cc",
     "context_menu_mus.h",
     "keyboard_ui_mus.cc",
     "keyboard_ui_mus.h",
     "pointer_watcher_delegate_mus.cc",
     "pointer_watcher_delegate_mus.h",
     "shelf_delegate_mus.cc",
     "shelf_delegate_mus.h",
     "shell_delegate_mus.cc",
     "shell_delegate_mus.h",
@@ skipping 95 matching lines @@
 
 repack("resources_200") {
   sources = [
     "$root_out_dir/ash_test_resources_200_percent.pak",
   ]
   output = "$root_out_dir/ash_resources_200_percent.pak"
   deps = [
     "//ash/resources:ash_test_resources_200_percent",
   ]
 }