[Media Router] (device discovery) Create MediaSinkService interface

chrome/browser/media/router/media_sink_service.h

+// 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.
+
+#ifndef CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINK_SERVICE_H_
+#define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINK_SERVICE_H_
+
+#include <memory>

[imcheng, 2017/02/07 19:25:31]

#include <vector>

[zhaobin, 2017/02/07 22:58:45]

Done.

+
+#include "base/callback.h"
+#include "chrome/browser/media/router/media_sink.h"
+
+namespace media_router {
+
+class MediaSinksObserver;
+
+// A service which can be used to start device discovery and resolution in the
+// background to generate MediaSinks. In addition, the service is capable of
+// answering MediaSink queries using the sinks that it generated. This class is

[imcheng, 2017/02/07 19:25:31]

nit: start the sentence about thread safety in a new line.

[zhaobin, 2017/02/07 22:58:45]

Done.

+// not thread safe. All methods must be called from the UI thread.
+class MediaSinkService {
+ public:
+  // Callback used for |Start()|.
+  // Arg 0: Sinks discovered and resolved by the service.
+  using OnSinksDiscoveredCallback =
+      base::Callback<void(const std::vector<MediaSink>&)>;

[imcheng, 2017/02/07 19:25:31]

Since we are defining subtypes of MediaSink in another patch, would this have to
become std::vector<std::unique_ptr<MediaSink>> to prevent object slicing?

[zhaobin, 2017/02/07 22:58:45]

Done.

+
+  virtual ~MediaSinkService() = default;
+
+  // Starts sink discovery. No-ops if already started.
+  // Sinks discovered and resolved are continuously passed to
+  // |callback|.
+  virtual void Start(const OnSinksDiscoveredCallback& callback) = 0;
+
+  // Adds a sink query to observe for MediaSink updates.
+  // Only one observer can be added for a given MediaSource.
+  // Start() must be called first. This class does not take
+  // ownership of |observer|.
+  virtual void AddSinkQuery(MediaSinksObserver* observer) = 0;
+
+  // Removes a sink query and stop observing for MediaSink updates.
+  virtual void RemoveSinkQuery(MediaSinksObserver* observer) = 0;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SINK_SERVICE_H_