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

net/http/http_proxy_client_socket.cc

Index: net/http/http_proxy_client_socket.cc
diff --git a/net/http/http_proxy_client_socket.cc b/net/http/http_proxy_client_socket.cc
index 47aaa7b8a46971f0abab4940f8d41f67395f8496..f9ba3b83fa0dc29c46121b9cfd68c31f809cacc2 100644
--- a/net/http/http_proxy_client_socket.cc
+++ b/net/http/http_proxy_client_socket.cc
@@ -201,6 +201,14 @@ base::TimeDelta HttpProxyClientSocket::GetConnectTimeMicros() const {
   return base::TimeDelta::FromMicroseconds(-1);
 }
 
+NextProto HttpProxyClientSocket::GetNegotiatedProtocol() const {
+  if (transport_.get() && transport_->socket()) {
+    return transport_->socket()->GetNegotiatedProtocol();
+  }
+  NOTREACHED();
+  return kProtoUnknown;
+}
+
 int HttpProxyClientSocket::Read(IOBuffer* buf, int buf_len,
                                 const CompletionCallback& callback) {
   DCHECK(user_callback_.is_null());