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

mojo/public/cpp/bindings/lib/control_message_proxy.h

Index: mojo/public/cpp/bindings/lib/control_message_proxy.h
diff --git a/mojo/public/cpp/bindings/lib/control_message_proxy.h b/mojo/public/cpp/bindings/lib/control_message_proxy.h
index c3260d1095f9dc65d8f9b82f551696af1be52627..35a409914180c6eca95eab1c65380963b0904dd0 100644
--- a/mojo/public/cpp/bindings/lib/control_message_proxy.h
+++ b/mojo/public/cpp/bindings/lib/control_message_proxy.h
@@ -7,6 +7,8 @@
 
 #include <stdint.h>
 
+#include <string>
+
 #include "base/callback.h"
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/lib/serialization_context.h"
@@ -28,6 +30,8 @@ class ControlMessageProxy {
   void RequireVersion(uint32_t version);
 
   void FlushForTesting();
+  void SendDisconnectReason(uint32_t custom_reason,
+                            const std::string& description);
 
   void OnConnectionError();