[Offline pages] Downloads UI: Adding bridge for issuing notifications

components/offline_pages/downloads/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.
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 # GYP: //components/offline_pages.gypi:offline_pages_ui_adapter
 static_library("offline_pages_ui_adapter") {
   sources = [
     "download_ui_adapter.cc",
     "download_ui_adapter.h",
     "download_ui_item.cc",
     "download_ui_item.h",
+    "offline_page_download_notifier.h",
   ]
 
   deps = [
     "//base",
     "//components/offline_pages:offline_pages",
     "//url",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "download_ui_adapter_unittest.cc",
   ]
 
   deps = [
     ":offline_pages_ui_adapter",
     "//base",
     "//base/test:test_support",
     "//components/offline_pages:offline_pages",
     "//components/offline_pages:test_support",
     "//testing/gtest",
   ]
 }