Mojo: Force folks to handle the return value of MessageReceiver::Accept{WithResponder}

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 <assert.h>
 
 #include <vector>
@@ skipping 65 matching lines @@
   MOJO_DISALLOW_COPY_AND_ASSIGN(Message);
 };
 
 class MessageReceiver {
  public:
   virtual ~MessageReceiver() {}
 
   // The receiver may mutate the given message.  Returns true if the message
   // was accepted and false otherwise, indicating that the message was invalid
   // or malformed.
-  virtual bool Accept(Message* message) = 0;
+  virtual bool Accept(Message* message) MOJO_WARN_UNUSED_RESULT = 0;
 
   // A variant on Accept that registers a MessageReceiver (known as the
   // responder) to handle the response message generated from the given
   // message. The responder's Accept method 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,
-                                   MessageReceiver* responder) = 0;
+  virtual bool AcceptWithResponder(
+      Message* message, MessageReceiver* 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.
 MojoResult ReadAndDispatchMessage(MessagePipeHandle handle,
                                   MessageReceiver* receiver,
                                   bool* receiver_result);
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_MESSAGE_H_