Mojo C++ bindings: support closing [Associated]InterfaceRequest with reason.

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

 // Copyright 2015 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_CONTROL_MESSAGE_PROXY_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_CONTROL_MESSAGE_PROXY_H_
 
 #include <stdint.h>
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/lib/serialization_context.h"
+#include "mojo/public/cpp/bindings/message.h"
 
 namespace mojo {
 
-class MessageReceiverWithResponder;
-
 namespace internal {
 
 // Proxy for request messages defined in interface_control_messages.mojom.
 class ControlMessageProxy {
  public:
   // Doesn't take ownership of |receiver|. It must outlive this object.
   explicit ControlMessageProxy(MessageReceiverWithResponder* receiver);
   ~ControlMessageProxy();
 
   void QueryVersion(const base::Callback<void(uint32_t)>& callback);
   void RequireVersion(uint32_t version);
 
   void FlushForTesting();
   void SendDisconnectReason(uint32_t custom_reason,
                             const std::string& description);
 
   void OnConnectionError();
 
+  static Message ConstructDisconnectReasonMessage(
+      uint32_t custom_reason,
+      const std::string& description);
+
  private:
   void RunFlushForTestingClosure();
 
   // Not owned.
   MessageReceiverWithResponder* receiver_;
-  SerializationContext context_;
   bool encountered_error_ = false;
 
   base::Closure run_loop_quit_closure_;
 
   DISALLOW_COPY_AND_ASSIGN(ControlMessageProxy);
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_CONTROL_MESSAGE_PROXY_H_