Fix memory leak in unittests with new Mojo EDK.

mojo/edk/system/message_pipe_dispatcher.cc

Index: mojo/edk/system/message_pipe_dispatcher.cc
diff --git a/mojo/edk/system/message_pipe_dispatcher.cc b/mojo/edk/system/message_pipe_dispatcher.cc
index 75f7227c9296e86531653c48bda07fc8ffd15453..b5bf7323282aeadafc3111a3461d034c6e142193 100644
--- a/mojo/edk/system/message_pipe_dispatcher.cc
+++ b/mojo/edk/system/message_pipe_dispatcher.cc
@@ -435,9 +435,14 @@ void MessagePipeDispatcher::CancelAllAwakablesNoLock() {
 }
 
 void MessagePipeDispatcher::CloseImplNoLock() {
-  lock().AssertAcquired();
+  lock().AssertAcquired();
+  // This early circuit fixes leak in unit tests. There's nothing to do in the
+  // posted task.
+  if (!transferable_ && non_transferable_state_ == CLOSED)
+    return;
+
   // We take a manual refcount because at shutdown, the task below might not get
-  // a chance to execute. If that happens, the RawChannel's will still call our
+  // a chance to execute. If that happens, the RawChannel will still call our
   // OnError method because it always runs (since it watches thread
   // destruction). So to avoid UAF, manually add a reference and only release it
   // if the task runs.