Don't rely on SSL cipher fallback in proxy auth.

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 ed8c8d3fb6027567221888b254887bf60e894490..dc864c6e2809683a5f4ea7e0983799d8758e4a19 100644
--- a/net/http/http_proxy_client_socket.cc
+++ b/net/http/http_proxy_client_socket.cc
@@ -255,8 +255,9 @@ int HttpProxyClientSocket::PrepareForAuthRestart() {
   if (!response_.headers.get())
     return ERR_CONNECTION_RESET;
 
-  // If the connection can't be reused, just return ERR_CONNECTION_CLOSED.
-  // The request should be retried at a higher layer.
+  // If the connection can't be reused, return
+  // ERR_UNABLE_TO_REUSE_CONNECTION_FOR_PROXY_AUTH.  The request will be retried
+  // at a higher layer.
   if (!response_.headers->IsKeepAlive() ||
       !http_stream_parser_->CanFindEndOfResponse() ||
       !transport_->socket()->IsConnected()) {