[mojo-edk] Add explicit message object APIs

mojo/edk/system/message_pipe_dispatcher.h

Index: mojo/edk/system/message_pipe_dispatcher.h
diff --git a/mojo/edk/system/message_pipe_dispatcher.h b/mojo/edk/system/message_pipe_dispatcher.h
index b457ab99f633d23e219dbcece6d59fc49cf3fbff..ae73024ee7bb61040038984f97e56245d71559aa 100644
--- a/mojo/edk/system/message_pipe_dispatcher.h
+++ b/mojo/edk/system/message_pipe_dispatcher.h
@@ -18,6 +18,7 @@
 namespace mojo {
 namespace edk {
 
+class MessageForTransit;
 class NodeController;
 class PortsMessage;
 
@@ -51,16 +52,14 @@ class MessagePipeDispatcher : public Dispatcher {
                    const Watcher::WatchCallback& callback,
                    uintptr_t context) override;
   MojoResult CancelWatch(uintptr_t context) override;
-  MojoResult WriteMessage(const void* bytes,
-                          uint32_t num_bytes,
-                          const DispatcherInTransit* dispatchers,
-                          uint32_t num_dispatchers,
+  MojoResult WriteMessage(std::unique_ptr<MessageForTransit> message,
                           MojoWriteMessageFlags flags) override;
-  MojoResult ReadMessage(void* bytes,
+  MojoResult ReadMessage(std::unique_ptr<MessageForTransit>* message,
                          uint32_t* num_bytes,
                          MojoHandle* handles,
                          uint32_t* num_handles,
-                         MojoReadMessageFlags flags) override;
+                         MojoReadMessageFlags flags,
+                         bool ignore_num_bytes) override;
   HandleSignalsState GetHandleSignalsState() const override;
   MojoResult AddAwakable(Awakable* awakable,
                          MojoHandleSignals signals,