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

net/spdy/spdy_proxy_client_socket.cc

Index: net/spdy/spdy_proxy_client_socket.cc
diff --git a/net/spdy/spdy_proxy_client_socket.cc b/net/spdy/spdy_proxy_client_socket.cc
index e5ef78c02b549be55c9e794356c9087e922ee797..7c8b06d36f7ee9a91f4ff79078c70a9e6fbbce82 100644
--- a/net/spdy/spdy_proxy_client_socket.cc
+++ b/net/spdy/spdy_proxy_client_socket.cc
@@ -170,6 +170,10 @@ base::TimeDelta SpdyProxyClientSocket::GetConnectTimeMicros() const {
   return base::TimeDelta::FromMicroseconds(-1);
 }
 
+NextProto SpdyProxyClientSocket::GetNegotiatedProtocol() const {
+  return kProtoUnknown;
+}
+
 int SpdyProxyClientSocket::Read(IOBuffer* buf, int buf_len,
                                 const CompletionCallback& callback) {
   DCHECK(read_callback_.is_null());