[Media Router] Convert to use typemaps for media_router.mojom.

chrome/browser/media/router/media_sink.cc

Index: chrome/browser/media/router/media_sink.cc
diff --git a/chrome/browser/media/router/media_sink.cc b/chrome/browser/media/router/media_sink.cc
index 1e4892f7408b0a5b25d84d04df3ed6f48f7e9237..96864354a79fb293077637247966f33bd0384a23 100644
--- a/chrome/browser/media/router/media_sink.cc
+++ b/chrome/browser/media/router/media_sink.cc
@@ -16,6 +16,8 @@ MediaSink::MediaSink(const MediaSink::Id& sink_id,
 
 MediaSink::MediaSink(const MediaSink& other) = default;
 
+MediaSink::MediaSink() {}
+
 MediaSink::~MediaSink() {
 }