[mojo-edk] Add explicit message object APIs

mojo/edk/system/dispatcher.h

Index: mojo/edk/system/dispatcher.h
diff --git a/mojo/edk/system/dispatcher.h b/mojo/edk/system/dispatcher.h
index e8bcf330c6437b501d0d9a19cba00284591c7cad..d809c3991c39bf6f05c1106625686f42953ab608 100644
--- a/mojo/edk/system/dispatcher.h
+++ b/mojo/edk/system/dispatcher.h
@@ -31,6 +31,7 @@ namespace edk {
 
 class Awakable;
 class Dispatcher;
+class MessageForTransit;
 
 using DispatcherVector = std::vector<scoped_refptr<Dispatcher>>;
 
@@ -76,17 +77,15 @@ class MOJO_SYSTEM_IMPL_EXPORT Dispatcher
 
   ///////////// Message pipe API /////////////
 
-  virtual MojoResult WriteMessage(const void* bytes,
-                                  uint32_t num_bytes,
-                                  const DispatcherInTransit* dispatchers,
-                                  uint32_t num_dispatchers,
+  virtual MojoResult WriteMessage(std::unique_ptr<MessageForTransit> message,
                                   MojoWriteMessageFlags flags);
 
-  virtual MojoResult ReadMessage(void* bytes,
+  virtual MojoResult ReadMessage(std::unique_ptr<MessageForTransit>* message,
                                  uint32_t* num_bytes,
                                  MojoHandle* handles,
                                  uint32_t* num_handles,
-                                 MojoReadMessageFlags flags);
+                                 MojoReadMessageFlags flags,
+                                 bool ignore_num_bytes);
 
   ///////////// Shared buffer API /////////////