Crash fix: HTTPS server responds with 407 through non-authenticating proxy.

net/http/http_network_transaction.cc

Index: net/http/http_network_transaction.cc
diff --git a/net/http/http_network_transaction.cc b/net/http/http_network_transaction.cc
index de9529ed6a5930ebe6cc132be37a5275a1435d4f..bc2d3225debcce2f182e1b4aea4ba757d4838eeb 100644
--- a/net/http/http_network_transaction.cc
+++ b/net/http/http_network_transaction.cc
@@ -1089,6 +1089,11 @@ int HttpNetworkTransaction::HandleAuthChallenge() {
   if (target == HttpAuth::AUTH_PROXY && proxy_info_.is_direct())
     return ERR_UNEXPECTED_PROXY_AUTH;
 
+  // This case can trigger when an HTTPS server responds with a 407 status
+  // code through a non-authenticating proxy.
+  if (!auth_controllers_[target].get())
+    return ERR_UNEXPECTED_PROXY_AUTH;
+
   int rv = auth_controllers_[target]->HandleAuthChallenge(
       headers, (request_->load_flags & LOAD_DO_NOT_SEND_AUTH_DATA) != 0, false,
       net_log_);