CPP bindings: DCHECK when a Callback is destructed without being invoked

mojo/public/cpp/bindings/message.h

 // 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_H_
 
 #include <vector>
 
 #include "mojo/public/cpp/bindings/lib/message_internal.h"
@@ skipping 88 matching lines @@
   // AcceptWithResponder or some time after its return.
   //
   // NOTE: Upon returning true, AcceptWithResponder assumes ownership of
   // |responder| and will delete it after calling |responder->Accept| or upon
   // its own destruction.
   //
   virtual bool AcceptWithResponder(Message* message, MessageReceiver* responder)
       MOJO_WARN_UNUSED_RESULT = 0;
 };
 
+// A MessageReceiver that is also able to provide status about the state
+// of the underlying MessagePipe to which it will be forwarding messages
+// received via the |Accept()| call.
+class MessageReceiverWithStatus : public MessageReceiver {
+ public:
+  ~MessageReceiverWithStatus() override {}
+
+  // Returns |true| if this MessageReceiver is currently bound to a MessagePipe,
+  // the pipe has not been closed, and the pipe has not encountered an error.
+  virtual bool IsValid() = 0;
+};
+
+// An alternative to MessageReceiverWithResponder for cases in which it
+// is necessary for the implementor of this interface to know about the status
+// of the MessagePipe which will carry the responses.
+class MessageReceiverWithResponderStatus : public MessageReceiver {
+ public:
+  ~MessageReceiverWithResponderStatus() override {}
+
+  // A variant on Accept that registers a MessageReceiverWithStatus (known as
+  // the responder) to handle the response message generated from the given
+  // message. Any of the responder's methods (Accept or IsValid) may be called
+  // during  AcceptWithResponder or some time after its return.
+  //
+  // NOTE: Upon returning true, AcceptWithResponder assumes ownership of
+  // |responder| and will delete it after calling |responder->Accept| or upon
+  // its own destruction.
+  //
+  virtual bool AcceptWithResponder(Message* message,
+                                   MessageReceiverWithStatus* responder)
+      MOJO_WARN_UNUSED_RESULT = 0;
+};
+
 // Read a single message from the pipe and dispatch to the given receiver.  The
 // receiver may be null, in which case the message is simply discarded.
 // Returns MOJO_RESULT_SHOULD_WAIT if the caller should wait on the handle to
 // become readable. Returns MOJO_RESULT_OK if a message was dispatched and
 // otherwise returns an error code if something went wrong.
 //
 // NOTE: The message hasn't been validated and may be malformed!
 MojoResult ReadAndDispatchMessage(MessagePipeHandle handle,
                                   MessageReceiver* receiver,
                                   bool* receiver_result);
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_H_