ProxyResolvingSocket: Some small cleanups

This is an application of review feedback from
https://chromium-review.googlesource.com/c/chromium/src/+/1310638
... that I somehow managed to forget to upload.

Change-Id: I972d4e5a8722d0f3ef2684587cdb4911636c1575
Reviewed-on: https://chromium-review.googlesource.com/c/1318358Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605799}

services/network/proxy_resolving_socket_factory_mojo.cc

@@ -32,9 +32,11 @@ void ProxyResolvingSocketFactoryMojo::CreateProxyResolvingSocket(
     CreateProxyResolvingSocketCallback callback) {
   std::unique_ptr<net::StreamSocket> net_socket =
       factory_impl_.CreateSocket(url, options && options->use_tls);
-  if (options && options->fake_tls_handshake)
+  if (options && options->fake_tls_handshake) {
+    DCHECK(!options->use_tls);
     net_socket = std::make_unique<jingle_glue::FakeSSLClientSocket>(
         std::move(net_socket));
+  }
 
   auto socket = std::make_unique<ProxyResolvingSocketMojo>(
       std::move(net_socket),

services/network/public/mojom/proxy_resolving_socket.mojom

@@ -43,6 +43,7 @@ struct ProxyResolvingSocketOptions {
   // Tries to do a fake TLS handshake on the connection.
   // This is sometimes used with XMPP to pass through proxies.
   // See jingle_glue::FakeSSLClientSocket for more details.
+  // Should not be used with |use_tls| set to true.
   bool fake_tls_handshake = false;
 };