Add virtual Initialize methods to PortAllocator and NetworkManager.

webrtc/base/network.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 45 matching lines @@
  public:
   virtual ~DefaultLocalAddressProvider() = default;
   // The default local address is the local address used in multi-homed endpoint
   // when the any address (0.0.0.0 or ::) is used as the local address. It's
   // important to check the return value as a IP family may not be enabled.
   virtual bool GetDefaultLocalAddress(int family, IPAddress* ipaddr) const = 0;
 };
 
 // Generic network manager interface. It provides list of local
 // networks.
+//
+// This class can be constructed on any thread, but every other method
+// (including the destructor) should be called on the same thread.

[pthatcher1, 2016/06/23 23:41:35]

Now it sounds like it should be on the same thread as the constructor thread. 
Perhaps just add "(which thread may be different than the thread its constructed
on)".

[Taylor Brandstetter, 2016/06/24 00:43:07]

Given the word "but" and the sentence below I think the meaning is clear enough.
But I revised it again, take a look...

+// This allows constructing a NetworkManager subclass on one thread and
+// passing it into an object that uses it on a different thread.
 class NetworkManager : public DefaultLocalAddressProvider {
  public:
   typedef std::vector<Network*> NetworkList;
 
   // This enum indicates whether adapter enumeration is allowed.
   enum EnumerationPermission {
     ENUMERATION_ALLOWED,  // Adapter enumeration is allowed. Getting 0 network
                           // from GetNetworks means that there is no network
                           // available.
     ENUMERATION_BLOCKED,  // Adapter enumeration is disabled.
                           // GetAnyAddressNetworks() should be used instead.
   };
 
   NetworkManager();
   ~NetworkManager() override;
 
   // Called when network list is updated.
   sigslot::signal0<> SignalNetworksChanged;
 
   // Indicates a failure when getting list of network interfaces.
   sigslot::signal0<> SignalError;
 
+  // This should be called on the NetworkManager's thread before the
+  // NetworkManager is used. Subclasses may override this if necessary.
+  virtual void Initialize() {}
+
   // Start/Stop monitoring of network interfaces
   // list. SignalNetworksChanged or SignalError is emitted immediately
   // after StartUpdating() is called. After that SignalNetworksChanged
   // is emitted whenever list of networks changes.
   virtual void StartUpdating() = 0;
   virtual void StopUpdating() = 0;
 
   // Returns the current list of networks available on this machine.
   // StartUpdating() must be called before this method is called.
   // It makes sure that repeated calls return the same object for a
@@ skipping 315 matching lines @@
   int preference_;
   bool active_ = true;
   uint16_t id_ = 0;
 
   friend class NetworkManager;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_NETWORK_H_