[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_sinks_observer.h

+// Copyright 2015 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.
+
+#ifndef CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINKS_OBSERVER_H_
+#define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINKS_OBSERVER_H_
+
+#include <vector>
+
+#include "chrome/browser/media/router/media_sink.h"
+#include "chrome/browser/media/router/media_source.h"
+
+namespace media_router {
+
+struct SinksQueryResult {
+  SinksQueryResult();
+  ~SinksQueryResult();
+
+  std::vector<MediaSink> sinks;
+};
+
+// Base class for observing when the collection of sinks compatible with
+// a MediaSource has been updated.
+// A MediaSinksObserver implementation can be registered to MediaRouter to
+// receive results. It can then interpret / process the results accordingly.
+class MediaSinksObserver {
+ public:
+  // Constructs an observer that will observe for sinks compatible
+  // with |source|.
+  explicit MediaSinksObserver(const MediaSource& source);
+  virtual ~MediaSinksObserver();
+
+  // This function is invoked when the list of sinks compatible
+  // with |source_| has been updated.
+  virtual void OnSinksReceived(const SinksQueryResult& result) {}
+
+  const MediaSource& source() const { return source_; }
+
+ private:
+  friend class MediaRouterImpl;
+
+  MediaSource source_;
+
+  // This field will be set by MediaRouterImpl, and must be false by
+  // this instance's destruction.
+  bool registered_;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINKS_OBSERVER_H_
+