Mojo C++ bindings: support disconnect with a reason.

mojo/public/cpp/bindings/lib/router.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/cpp/bindings/lib/router.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 309 matching lines @@
   }
 
   control_message_proxy_.OnConnectionError();
 
   encountered_error_ = true;
 
   // The callbacks may hold on to resources. There is no need to keep them any
   // longer.
   async_responders_.clear();
 
-  if (!error_handler_.is_null())
+  if (!error_handler_.is_null()) {
     error_handler_.Run();
+  } else if (!error_with_reason_handler_.is_null()) {
+    // Make a copy on the stack. If we directly pass a reference to a member of
+    // |control_message_handler_|, that reference will be invalidated as soon as
+    // the user destroys the interface endpoint.
+    std::string description = control_message_handler_.disconnect_description();
+    error_with_reason_handler_.Run(
+        control_message_handler_.disconnect_custom_reason(), description);
+  }
 }
 
 // ----------------------------------------------------------------------------
 
 }  // namespace internal
 }  // namespace mojo