Mojo C++ bindings: support closing [Associated]InterfaceRequest with 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 35a409914180c6eca95eab1c65380963b0904dd0..557d5297288579d77ed64a7aa6609b7bf4c9ff92 100644
--- a/mojo/public/cpp/bindings/lib/control_message_proxy.h
+++ b/mojo/public/cpp/bindings/lib/control_message_proxy.h
@@ -12,11 +12,10 @@
 #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.
@@ -35,12 +34,15 @@ class ControlMessageProxy {
 
   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_;