Add virtual Initialize methods to PortAllocator and NetworkManager.

webrtc/base/network.h

Index: webrtc/base/network.h
diff --git a/webrtc/base/network.h b/webrtc/base/network.h
index 05943fb9125ea23f9cc24cf7f30f45a7841175ee..fe51e4eafb62f7467a1c9467968a7e6216795fb7 100644
--- a/webrtc/base/network.h
+++ b/webrtc/base/network.h
@@ -63,6 +63,13 @@ class DefaultLocalAddressProvider {
 
 // Generic network manager interface. It provides list of local
 // networks.
+//
+// Every method of NetworkManager (including the destructor) must be called on
+// the same thread, except for the constructor which may be called on any
+// thread.
+//
+// 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;
@@ -85,6 +92,10 @@ class NetworkManager : public DefaultLocalAddressProvider {
   // 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