[mojo-edk] Add explicit message object APIs

mojo/edk/system/dispatcher.cc

Index: mojo/edk/system/dispatcher.cc
diff --git a/mojo/edk/system/dispatcher.cc b/mojo/edk/system/dispatcher.cc
index cade21570d485d6932723352507ed426aef1cbc6..973a354839f47547e36ad82967c4bccc55b31d9f 100644
--- a/mojo/edk/system/dispatcher.cc
+++ b/mojo/edk/system/dispatcher.cc
@@ -32,19 +32,17 @@ MojoResult Dispatcher::CancelWatch(uintptr_t context) {
   return MOJO_RESULT_INVALID_ARGUMENT;
 }
 
-MojoResult Dispatcher::WriteMessage(const void* bytes,
-                                    uint32_t num_bytes,
-                                    const DispatcherInTransit* dispatchers,
-                                    uint32_t num_dispatchers,
+MojoResult Dispatcher::WriteMessage(std::unique_ptr<MessageForTransit> message,
                                     MojoWriteMessageFlags flags) {
   return MOJO_RESULT_INVALID_ARGUMENT;
 }
 
-MojoResult Dispatcher::ReadMessage(void* bytes,
+MojoResult Dispatcher::ReadMessage(std::unique_ptr<MessageForTransit>* message,
                                    uint32_t* num_bytes,
                                    MojoHandle* handles,
                                    uint32_t* num_handles,
-                                   MojoReadMessageFlags flags) {
+                                   MojoReadMessageFlags flags,
+                                   bool ignore_num_bytes) {
   return MOJO_RESULT_INVALID_ARGUMENT;
 }