Add a floating close button for arc custom notification

ui/arc/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("//testing/test.gni")
 
 static_library("arc") {
   sources = [
     "notification/arc_custom_notification_item.cc",
     "notification/arc_custom_notification_item.h",
     "notification/arc_custom_notification_view.cc",
     "notification/arc_custom_notification_view.h",
     "notification/arc_notification_item.cc",
     "notification/arc_notification_item.h",
     "notification/arc_notification_manager.cc",
     "notification/arc_notification_manager.h",
     "notification/arc_notification_surface_manager.cc",
     "notification/arc_notification_surface_manager.h",
   ]
 
   deps = [
+    "//ash:ash",
     "//base",
+    "//components/arc:arc_base",
     "//components/arc:arc_bindings",
+    "//components/exo:exo",
     "//components/signin/core/account_id",
     "//skia",
+    "//ui/base",
     "//ui/gfx",
     "//ui/message_center",
+    "//ui/resources",
+    "//ui/strings",
+    "//ui/views",
   ]
 }
 
 test("ui_arc_unittests") {
   testonly = true
   sources = [
     "notification/arc_notification_manager_unittest.cc",
     "test/run_all_unittests.cc",
   ]
 
   deps = [
     ":arc",
     "//base",
     "//base/test:test_support",
     "//components/arc:arc_test_support",
     "//mojo/edk/system",
+    "//testing/gtest",
     "//ui/message_center:test_support",
   ]
 }