Add virtual Initialize methods to PortAllocator and NetworkManager.

webrtc/api/peerconnection.cc

Index: webrtc/api/peerconnection.cc
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index b9cb83e724de78db6683bd0dc242afb6d80a928a..fcce03d5c0c1bf7c19670b64102a7b1effcaaacd 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -2139,6 +2139,8 @@ bool PeerConnection::InitializePortAllocator_n(
     return false;
   }
 
+  port_allocator_->Initialize();
+
   // To handle both internal and externally created port allocator, we will
   // enable BUNDLE here.
   int portallocator_flags = port_allocator_->flags();