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 182be87d58cfdab1fb2a5837f38e640b51e710e1..c0ba9d1051e054f5031d0229909ef8a8600534ca 100644
--- a/net/spdy/spdy_proxy_client_socket.cc
+++ b/net/spdy/spdy_proxy_client_socket.cc
@@ -169,6 +169,10 @@ 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());