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

mojo/edk/system/message_pipe_dispatcher.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/edk/system/message_pipe_dispatcher.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "mojo/edk/system/configuration.h"
@@ skipping 115 matching lines @@
 }
 
 void MessagePipeDispatcher::CloseImplNoLock() {
   mutex().AssertHeld();
   message_pipe_->Close(port_);
   message_pipe_ = nullptr;
   port_ = kInvalidPort;
 }
 
 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.
   auto dispatcher = MessagePipeDispatcher::Create(kDefaultCreateOptions);
   dispatcher->Init(std::move(message_pipe_), port_);
   port_ = kInvalidPort;
   return dispatcher;
 }
 
 MojoResult MessagePipeDispatcher::WriteMessageImplNoLock(
@@ skipping 64 matching lines @@
     std::vector<ScopedPlatformHandle>* platform_handles) {
   AssertHasOneRef();  // Only one ref => no need to take the lock.
 
   bool rv = message_pipe_->EndSerialize(port_, channel, destination,
                                         actual_size, platform_handles);
   message_pipe_ = nullptr;
   port_ = kInvalidPort;
   return rv;
 }
 
-// MessagePipeDispatcherTransport ----------------------------------------------
-
-MessagePipeDispatcherTransport::MessagePipeDispatcherTransport(
-    DispatcherTransport transport)
-    : DispatcherTransport(transport) {
-  DCHECK_EQ(message_pipe_dispatcher()->GetType(),
-            Dispatcher::Type::MESSAGE_PIPE);
-}
-
 }  // namespace system
 }  // namespace mojo