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..a8cfb6919423fe3c00748229364ba550e094ece5 100644
--- a/webrtc/base/network.h
+++ b/webrtc/base/network.h
@@ -63,6 +63,11 @@ class DefaultLocalAddressProvider {
 
 // 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 a different thread.

[pthatcher1, 2016/06/23 22:01:59]

This makes it sound like it must be constructed and used on different threads. 
But what I think you mean to say is that it must be used only on one thread, but
that thread can be different than the thread it's constructed on.  Is that
right?

[Taylor Brandstetter, 2016/06/23 22:59:07]

Good catch. Just a situation where my brain was working faster than my fingers.
I mean to say "on the same thread" here and "on a different thread" below but I
accidentally typed the latter in both places.

+// 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 +90,10 @@ 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