[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 {

[mark a. foltz, 2015/03/27 21:21:59]

Should this be a using declaration for std::vector<MediaSink> instead of a
struct?
Or do we want the flexibility to add additional data over time?

[imcheng, 2015/03/30 22:49:10]

The latter.

+  SinksQueryResult();
+  ~SinksQueryResult();
+
+  std::vector<MediaSink> sinks;
+};
+
+// Interface for observing when the collection of sinks compatible with

[mark a. foltz, 2015/03/27 21:21:59]

Not an interface.

[imcheng, 2015/03/30 22:49:10]

Ok, let's call it base class and provide a no-op implementation for
OnSinksReceived.

+// 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) : source_(source) {}
+  virtual ~MediaSinksObserver() {}
+
+  // This function is invoked when the list of sinks compatible
+  // with |source_| has been updated.
+  virtual void OnSinksReceived(const SinksQueryResult& result) = 0;

[mark a. foltz, 2015/03/27 21:21:59]

The API is a little limiting in that there must be one observer object per
source.  If we wanted a true observer interface it might look like:

virtual void OnSinksReceived(const MediaSource& source, const SinksQueryResult&
result)

[imcheng, 2015/03/30 22:49:10]

Agreed. WebContentsObserver follow a similar model, vs. the older
NotificationRegistrar model. We can change it from single-target to the API you
described (with the observer implementation doing the filtering instead of the
MR) if it turns out to be more convenient.

+
+  const MediaSource& source() const { return source_; }
+
+ private:
+  MediaSource source_;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINKS_OBSERVER_H_