Remove -Wno-reorder from examples/BUILD.gn.

Bug: webrtc:9251
Change-Id: I447469e94ad938eaaa628edcd1a57cdeac6ed603
Reviewed-on: https://webrtc-review.googlesource.com/88123
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23928}

examples/peerconnection/client/main_wnd.cc

@@ -81,8 +81,8 @@ MainWnd::MainWnd(const char* server,
       button_(NULL),
       listbox_(NULL),
       destroyed_(false),
-      callback_(NULL),
       nested_msg_(NULL),
+      callback_(NULL),
       server_(server),
       auto_connect_(auto_connect),
       auto_call_(auto_call) {