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

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 005b0948e740a0dd356c34fcb2fe44e922e9d09a..a0d5d02b62dead1c22f9ad19f8ae2f4b4dcf6aeb 100644
--- a/mojo/edk/system/message_pipe_dispatcher.cc
+++ b/mojo/edk/system/message_pipe_dispatcher.cc
@@ -133,9 +133,22 @@ void MessagePipeDispatcher::CloseImplNoLock() {
 }
 
 RefPtr<Dispatcher>
-MessagePipeDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock() {
+MessagePipeDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock(
+    MessagePipe* message_pipe,
+    unsigned port) {
   mutex().AssertHeld();
 
+  // "We" are being sent over our peer.
+  if (message_pipe == message_pipe_.get()) {
+    // A message pipe dispatcher can't be sent over itself (this should be
+    // disallowed by |Core|). Note that |port| is the destination port.
+    DCHECK_EQ(port, port_);
+    // In this case, |message_pipe_|'s mutex should already be held!
+    message_pipe_->CancelAllAwakablesNoLock(port_);
+  } else {
+    CancelAllAwakablesNoLock();
+  }
+
   // TODO(vtl): Currently, there are no options, so we just use
   // |kDefaultCreateOptions|. Eventually, we'll have to duplicate the options
   // too.
@@ -220,14 +233,5 @@ bool MessagePipeDispatcher::EndSerializeAndCloseImplNoLock(
   return rv;
 }
 
-// MessagePipeDispatcherTransport ----------------------------------------------
-
-MessagePipeDispatcherTransport::MessagePipeDispatcherTransport(
-    DispatcherTransport transport)
-    : DispatcherTransport(transport) {
-  DCHECK_EQ(message_pipe_dispatcher()->GetType(),
-            Dispatcher::Type::MESSAGE_PIPE);
-}
-
 }  // namespace system
 }  // namespace mojo