Adding PortAllocator option to support cases where sockets can't be bound.

webrtc/base/network.h

Index: webrtc/base/network.h
diff --git a/webrtc/base/network.h b/webrtc/base/network.h
index 52d7d35a2c924e5dcfa6fcf808128dcfaa42e7ff..34d6538c33c071245966d4f3184b3fcfce015889 100644
--- a/webrtc/base/network.h
+++ b/webrtc/base/network.h
@@ -118,6 +118,10 @@ class NetworkManager : public DefaultLocalAddressProvider {
   // IP address.  (i.e. INADDR_ANY for IPv4 or in6addr_any for IPv6). This is
   // useful as binding to such interfaces allow default routing behavior like
   // http traffic.
+  //
+  // This method appends the "any address" networks to the list, such that this
+  // can optionally be called after GetNetworks.
+  //
   // TODO(guoweis): remove this body when chromium implements this.
   virtual void GetAnyAddressNetworks(NetworkList* networks) {}