[Media Router] Add MediaSink subtypes

chrome/browser/media/router/dial_media_sink.cc

+// 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.
+
+#include "chrome/browser/media/router/dial_media_sink.h"
+
+#include "base/logging.h"
+
+namespace media_router {
+
+DialMediaSink::DialMediaSink(const MediaSink::Id& sink_id,
+                             const std::string& name,
+                             const MediaSink::IconType icon_type)
+    : MediaSink(sink_id, name, icon_type) {
+  type_ = SinkType::DIAL;
+}
+
+DialMediaSink::DialMediaSink(const DialMediaSink& other) = default;
+
+DialMediaSink::~DialMediaSink() = default;
+
+// static
+const DialMediaSink* DialMediaSink::Cast(const MediaSink* sink) {
+  DCHECK(sink->type() == MediaSink::SinkType::DIAL);
+  return static_cast<const DialMediaSink*>(sink);
+}
+
+// static
+DialMediaSink* DialMediaSink::Cast(MediaSink* sink) {
+  DCHECK(sink->type() == MediaSink::SinkType::DIAL);
+  return static_cast<DialMediaSink*>(sink);
+}
+
+}  // namespace media_router