Make it possible to write a message pipe endpoint's peer into it.

mojo/edk/system/data_pipe_consumer_dispatcher.cc

Index: mojo/edk/system/data_pipe_consumer_dispatcher.cc
diff --git a/mojo/edk/system/data_pipe_consumer_dispatcher.cc b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
index 521456efcbb3f86ab1dc77bf147eb563977050ac..cdf553fb35230f9a88f02e1a0dcf13ebceeeaa38 100644
--- a/mojo/edk/system/data_pipe_consumer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
@@ -72,9 +72,13 @@ void DataPipeConsumerDispatcher::CloseImplNoLock() {
 }
 
 RefPtr<Dispatcher>
-DataPipeConsumerDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock() {
+DataPipeConsumerDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock(
+    MessagePipe* /*message_pipe*/,
+    unsigned /*port*/) {
   mutex().AssertHeld();
 
+  CancelAllAwakablesNoLock();
+
   auto dispatcher = DataPipeConsumerDispatcher::Create();
   dispatcher->Init(std::move(data_pipe_));
   return dispatcher;