[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;
+};

[xhwang, 2015/04/02 17:13:03]

Do you plan to add more values to the result? Can we just return
std::vector<MediaSink> as the result?

[imcheng, 2015/04/02 23:05:24]

Right now we don't plan to add any more. I am not sure on the likelihood that we
will add more in the future. So it should be fine to just return the vector.

+
+// 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;

[xhwang, 2015/04/02 17:13:03]

MediaSinksObserver seems to be an interface, but we are exposing a lot of
details: source() which is public and registered_ through friend. Does
MediaRouter care about these?

[imcheng, 2015/04/02 23:05:24]

Yes. source() by media router in determining the sink query to send to media
route provider manager. registered_ is a safeguard that we don't have dangling
observer pointers.

[xhwang, 2015/04/06 20:51:30]

How do you plan implement "MediaRouter send updates with media sinks that are
compatible with that source"? Will you check call "source()" on each observer
and compare it with the "source" of the update? In that case, can you pass
source() to MediaRouter at registration time, so that MediaRouter can find the
observers more quickly, and you don't have to expose source() here?

[imcheng, 2015/04/06 21:54:20]

MediaRouter will keep a map from source to a set of observers for that source.
When updates come in, the MediaRouter impl will look up the same for the set of
observers to notify.

+
+  MediaSource source_;
+
+  // Whether the observer is registered to the Media Router.
+  // This field will be set by MediaRouterImpl, and must be false by
+  // this instance's destruction. This is used to detect if the observer
+  // is being destroyed while still registered to the Media Router.
+  bool registered_;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINKS_OBSERVER_H_
+