[Media Router] Create MediaSinkServiceBase and make DialMediaSinkService inherit from it

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_service.cc",
     "dial/device_description_service.h",
     "dial/dial_device_data.cc",
     "dial/dial_device_data.h",
-    "dial/dial_media_sink_service.cc",
-    "dial/dial_media_sink_service.h",
+    "dial/dial_media_sink_service_impl.cc",
+    "dial/dial_media_sink_service_impl.h",
     "dial/dial_registry.cc",
     "dial/dial_registry.h",
     "dial/dial_service.cc",
     "dial/dial_service.h",
     "dial/parsed_dial_device_description.cc",
     "dial/parsed_dial_device_description.h",
     "dial/safe_dial_device_description_parser.cc",
     "dial/safe_dial_device_description_parser.h",
     "mdns/dns_sd_delegate.cc",
     "mdns/dns_sd_delegate.h",
     "mdns/dns_sd_device_lister.cc",
     "mdns/dns_sd_device_lister.h",
     "mdns/dns_sd_registry.cc",
     "mdns/dns_sd_registry.h",
+    "media_sink_service_base.cc",
+    "media_sink_service_base.h",
   ]
 }