Add DiscoveryNetworkMonitor implementation

chrome/browser/media/router/discovery/discovery_network_monitor.h

+// Copyright (c) 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_DISCOVERY_DISCOVERY_NETWORK_MONITOR_H_
+#define CHROME_BROWSER_MEDIA_ROUTER_DISCOVERY_DISCOVERY_NETWORK_MONITOR_H_
+
+#include <string>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/lazy_instance.h"
+#include "base/macros.h"
+#include "base/observer_list_threadsafe.h"
+#include "base/synchronization/lock.h"
+#include "chrome/browser/media/router/discovery/discovery_network_info.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/ip_address.h"
+#include "net/base/network_change_notifier.h"
+
+// Tracks the set of active network interfaces that can be used for local
+// discovery.  If the list of interfaces changes, then
+// DiscoveryNetworkMonitor::Observer is called with the instance of the monitor.
+// Only one instance of this should be created per browser process.
+//
+// This class is not thread-safe, except for adding and removing observers.
+// Most of the work done by the monitor is done on the IO thread, which includes
+// updating the current network ID.  Therefore |GetNetworkId| should only be
+// called from the IO thread.  All observers will be notified of network changes
+// on the thread from which they registered.
+class DiscoveryNetworkMonitor
+    : public net::NetworkChangeNotifier::NetworkChangeObserver {
+ public:
+  using NetworkInfoCallback =
+      base::Callback<std::vector<DiscoveryNetworkInfo>()>;
+  using NetworkRefreshCompleteCallback = base::Callback<void()>;
+  class Observer {
+   public:
+    // Called when the list of connected interfaces has changed.
+    virtual void OnNetworksChanged(const DiscoveryNetworkMonitor& monitor) = 0;
+
+   protected:
+    ~Observer() = default;
+  };
+
+  static DiscoveryNetworkMonitor* GetInstance();
+  static DiscoveryNetworkMonitor* GetInstanceForTest(NetworkInfoCallback);
+
+  void RebindNetworkChangeObserverForTest();
+
+  void AddObserver(Observer* const observer);
+  void RemoveObserver(Observer* const observer);
+
+  // Forces a query of the current network state.  |callback| will be called
+  // after the refresh.  This should be called from the UI thread.
+  void Refresh(NetworkRefreshCompleteCallback callback);

[imcheng, 2017/05/26 23:49:01]

|callback| could be const ref?

[btolsch, 2017/05/30 09:54:30]

From //docs/callback.md, base::Callback should be passed by value when ownership
is transferred, e.g. passing to PostTask or running directly.

+
+  // Computes a stable string identifier from the list of connected interfaces.
+  // Returns kNetworkIdDisconnected if there are no connected interfaces or
+  // kNetworkIdUnknown if the identifier could not be computed.  This should be
+  // called from the IO thread.
+  const std::string& GetNetworkId() const;
+
+  // Constants for the special states of network Id.

[mark a. foltz, 2017/05/26 21:38:55]

Constants should be declared before functions:

https://google.github.io/styleguide/cppguide.html#Declaration_Order

[btolsch, 2017/05/26 23:38:10]

Done.

+  static const char kNetworkIdDisconnected[];
+  static const char kNetworkIdUnknown[];
+
+ private:
+  friend struct base::LazyInstanceTraitsBase<DiscoveryNetworkMonitor>;
+
+  DiscoveryNetworkMonitor();
+  ~DiscoveryNetworkMonitor() override;
+
+  // net::NetworkChangeNotifier::NetworkChangeObserver
+  void OnNetworkChanged(
+      net::NetworkChangeNotifier::ConnectionType type) override;
+
+  void UpdateNetworkInfo(const NetworkRefreshCompleteCallback& callback);
+
+  std::string network_id_;

[mark a. foltz, 2017/05/26 21:38:55]

Can you add documentation for these fields?

[btolsch, 2017/05/26 23:38:10]

Done.

+  std::vector<DiscoveryNetworkInfo> networks_;
+  scoped_refptr<base::ObserverListThreadSafe<Observer>> observers_;
+  NetworkInfoCallback network_info_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscoveryNetworkMonitor);
+};
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_DISCOVERY_DISCOVERY_NETWORK_MONITOR_H_