Add missing header files to GN files

chrome/browser/media/router/discovery/BUILD.gn

 # Copyright 2017 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.
 #
 
 static_library("discovery") {
   inputs = [
     "$root_gen_dir/chrome/grit/generated_resources.h",
   ]
   deps = [
     "//base",
     "//base:i18n",
     "//chrome/app:generated_resources",
     "//chrome/common:constants",
     "//content/public/browser",
     "//content/public/common",
   ]
   sources = [
     "dial/device_description_fetcher.cc",
-    "dial/device_description_fetcher.h ",
+    "dial/device_description_fetcher.h",
     "dial/dial_device_data.cc",
     "dial/dial_device_data.h",
     "dial/dial_registry.cc",
     "dial/dial_registry.h",
     "dial/dial_service.cc",
     "dial/dial_service.h",
     "dial/safe_dial_device_description_parser.cc",
     "dial/safe_dial_device_description_parser.h",
   ]
 }