Do not use QUIC for requests that are through a proxy.

net/http/http_stream_factory_impl_job.cc

Index: net/http/http_stream_factory_impl_job.cc
diff --git a/net/http/http_stream_factory_impl_job.cc b/net/http/http_stream_factory_impl_job.cc
index 09b58d403e7b193bfc41f4f77e04d99d48502c86..9fd44734269920abbad43e0f3433454d74f37d36 100644
--- a/net/http/http_stream_factory_impl_job.cc
+++ b/net/http/http_stream_factory_impl_job.cc
@@ -668,6 +668,11 @@ int HttpStreamFactoryImpl::Job::DoResolveProxyComplete(int result) {
       // No proxies/direct to choose from. This happens when we don't support
       // any of the proxies in the returned list.
       result = ERR_NO_SUPPORTED_PROXIES;
+    } else if (using_quic_ &&
+               (!proxy_info_.is_quic() && !proxy_info_.is_direct())) {
+      // QUIC can not be spoken to non-QUIC proxies.  This error should not be
+      // user visible, because the non-alternate job should be resumed.
+      result = ERR_NO_SUPPORTED_PROXIES;
     }
   }