Adding platform support check for NetworkObserver

net/base/network_change_notifier.h

 // Copyright (c) 2012 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 NET_BASE_NETWORK_CHANGE_NOTIFIER_H_
 #define NET_BASE_NETWORK_CHANGE_NOTIFIER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 273 matching lines @@
   // type.
   static void GetMaxBandwidthAndConnectionType(double* max_bandwidth_mbps,
                                                ConnectionType* connection_type);
 
   // Returns a theoretical upper limit (in Mbps) on download bandwidth given a
   // connection subtype. The mapping of connection type to maximum bandwidth is
   // provided in the NetInfo spec: http://w3c.github.io/netinfo/.
   // TODO(jkarlin): Rename to GetMaxBandwidthMbpsForConnectionSubtype.
   static double GetMaxBandwidthForConnectionSubtype(ConnectionSubtype subtype);
 
+  // Returns true if the platform supports use of APIs based on NetworkHandles.
+  // Public methods that use NetworkHandles are GetNetworkConnectionType(),
+  // GetNetworkConnectionType(), GetDefaultNetwork(), AddNetworkObserver(),
+  // RemoveNetworkObserver(), and all public NetworkObserver methods.
+  static bool AreNetworkHandlesSupported();
+
   // Sets |network_list| to a list of all networks that are currently connected.
   // Only implemented for Android (Lollipop and newer), leaves |network_list|
-  // empty when unimplemented.
+  // empty when unimplemented. Requires NetworkHandles support, see
+  // AreNetworkHandlesSupported().
   static void GetConnectedNetworks(NetworkList* network_list);
 
   // Returns the type of connection |network| uses. Note that this may vary
   // slightly over time (e.g. CONNECTION_2G to CONNECTION_3G). If |network|
   // is no longer connected, it will return CONNECTION_UNKNOWN.
   // Only implemented for Android (Lollipop and newer), returns
-  // CONNECTION_UNKNOWN when unimplemented.
+  // CONNECTION_UNKNOWN when unimplemented. Requires NetworkHandles support,
+  // see AreNetworkHandlesSupported().
   static ConnectionType GetNetworkConnectionType(NetworkHandle network);
 
   // Returns the device's current default network connection. This is the
   // network used for newly created socket communication for sockets that are
   // not explicitly bound to a particular network (e.g. via
   // DatagramClientSocket.BindToNetwork). Returns |kInvalidNetworkHandle| if
   // there is no default connected network.
   // Only implemented for Android (Lollipop and newer), returns
   // |kInvalidNetworkHandle| when unimplemented.
+  // Requires NetworkHandles support, see AreNetworkHandlesSupported().
   static NetworkHandle GetDefaultNetwork();
 
   // Retrieve the last read DnsConfig. This could be expensive if the system has
   // a large HOSTS file.
   static void GetDnsConfig(DnsConfig* config);
 
 #if defined(OS_LINUX)
   // Returns the AddressTrackerLinux if present.
   static const internal::AddressTrackerLinux* GetAddressTracker();
 #endif
@@ skipping 151 matching lines @@
 #endif
 
   // These are the actual implementations of the static queryable APIs.
   // See the description of the corresponding functions named without "Current".
   // Implementations must be thread-safe. Implementations must also be
   // cheap as they are called often.
   virtual ConnectionType GetCurrentConnectionType() const = 0;
   virtual void GetCurrentMaxBandwidthAndConnectionType(
       double* max_bandwidth_mbps,
       ConnectionType* connection_type) const;
+  virtual bool AreNetworkHandlesCurrentlySupported() const;
   virtual void GetCurrentConnectedNetworks(NetworkList* network_list) const;
   virtual ConnectionType GetCurrentNetworkConnectionType(
       NetworkHandle network) const;
   virtual NetworkHandle GetCurrentDefaultNetwork() const;
 
   // Broadcasts a notification to all registered observers.  Note that this
   // happens asynchronously, even for observers on the current thread, even in
   // tests.
   static void NotifyObserversOfIPAddressChange();
   static void NotifyObserversOfConnectionTypeChange();
@@ skipping 54 matching lines @@
 
   // Set true to disable non-test notifications (to prevent flakes in tests).
   static bool test_notifications_only_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifier);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_CHANGE_NOTIFIER_H_