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

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 18bd1fadc6ebda3add5e781dda4aaa7c423fb572..4bbd1dae2dbe3c0eb9b8cdc64b72d79d28721e41 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -3645,9 +3645,10 @@ test("unit_tests") {
       "../browser/media/router/discovery/dial/device_description_fetcher_unittest.cc",
       "../browser/media/router/discovery/dial/device_description_service_unittest.cc",
       "../browser/media/router/discovery/dial/dial_device_data_unittest.cc",
-      "../browser/media/router/discovery/dial/dial_media_sink_service_unittest.cc",
+      "../browser/media/router/discovery/dial/dial_media_sink_service_impl_unittest.cc",
       "../browser/media/router/discovery/dial/dial_registry_unittest.cc",
       "../browser/media/router/discovery/dial/dial_service_unittest.cc",
+      "../browser/media/router/discovery/media_sink_service_base_unittest.cc",
 
       # TODO(crbug.com/646627):
       # Move media_router_ui_service_factory_unittest.cc to chrome/browser/ui.