Add a new GetNegotiatedProtocol method to StreamSocket and implement in all subclasses.

net/socket/stream_socket.h

Index: net/socket/stream_socket.h
diff --git a/net/socket/stream_socket.h b/net/socket/stream_socket.h
index d9fee24cebb9642314e08cb2ff05ad54fde27a1c..25fce1797faee8aad8064bf5a71721880a83ee01 100644
--- a/net/socket/stream_socket.h
+++ b/net/socket/stream_socket.h
@@ -87,6 +87,10 @@ class NET_EXPORT_PRIVATE StreamSocket : public Socket {
   // Returns the connection setup time of this socket.
   virtual base::TimeDelta GetConnectTimeMicros() const = 0;
 
+  // Returns the protocol negotiated via for this socket, or

[Sergey Ulanov, 2012/04/02 18:20:22]

via NPN?

[Ryan Hamilton, 2012/04/02 20:57:33]

Done.

+  // kProtoUnknown will be returned if NPN is not applicable.

[Sergey Ulanov, 2012/04/02 18:20:22]

I think ideally this shouldn't be part of StreamSocket interface. Can we make a
separate interface called NegotiatingStreamSocket  or NpnStreamSocket that would
inherit from StreamSocket and add this method? That way you wouldn't have to fix
every single implementation of StreamSocket interface. 

[Ryan Hamilton, 2012/04/02 20:57:33]

Yeah, I totally hear you.  The problem comes up because SPDY sessions can be
layered on top of pretty much any kind of socket.  SSL sockets and HTTP proxy
sockets both have the ability to negotiate the SPDY protocol.  However, SPDY
(via command line flags) can also live on top of, for example, a TCP socket.

This seems to imply that pretty much any StreamSocket subclass that SPDY session
can be layered on would need to extend this new class.  But that would be
roughly all of them :| 

It's definitely a thorny issue and we talked about it quite a bit internally.  I
also just chatted with wtc again after reading your comment.  We wish there were
a cleaner solution, but feel that this CL is about as good as we're going to
get.

+  virtual NextProto GetNegotiatedProtocol() const = 0;
+
  protected:
   // The following class is only used to gather statistics about the history of
   // a socket.  It is only instantiated and used in basic sockets, such as