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

net/socket/buffered_write_stream_socket.cc

Index: net/socket/buffered_write_stream_socket.cc
diff --git a/net/socket/buffered_write_stream_socket.cc b/net/socket/buffered_write_stream_socket.cc
index 94c6d573d93c01c7f148b8e436e15f76abb58fab..028dfde2eb0e22febc1eca9faf5f87cf3655c8f7 100644
--- a/net/socket/buffered_write_stream_socket.cc
+++ b/net/socket/buffered_write_stream_socket.cc
@@ -119,6 +119,10 @@ base::TimeDelta BufferedWriteStreamSocket::GetConnectTimeMicros() const {
   return wrapped_socket_->GetConnectTimeMicros();
 }
 
+NextProto BufferedWriteStreamSocket::GetNegotiatedProtocol() const {
+  return wrapped_socket_->GetNegotiatedProtocol();
+}
+
 void BufferedWriteStreamSocket::DoDelayedWrite() {
   int result = wrapped_socket_->Write(
       io_buffer_, io_buffer_->RemainingCapacity(),