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

mojo/edk/system/message_pipe.h

 // 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.
 
 #ifndef MOJO_EDK_SYSTEM_MESSAGE_PIPE_H_
 #define MOJO_EDK_SYSTEM_MESSAGE_PIPE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 99 matching lines @@
                       Channel* channel,
                       size_t* max_size,
                       size_t* max_platform_handles);
   bool EndSerialize(
       unsigned port,
       Channel* channel,
       void* destination,
       size_t* actual_size,
       std::vector<platform::ScopedPlatformHandle>* platform_handles);
 
+  // This "implements" |CancelAllAwakables()|, but assumes that |mutex_| is
+  // already held. This is for use by
+  // |MessagePipeDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock()|.
+  void CancelAllAwakablesNoLock(unsigned port)
+      MOJO_EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+
   // |ChannelEndpointClient| methods:
   bool OnReadMessage(unsigned port, MessageInTransit* message) override;
   void OnDetachFromChannel(unsigned port) override;
 
  private:
   MessagePipe();
   ~MessagePipe() override;
 
   // This is used internally by |WriteMessage()| and by |OnReadMessage()|.
   // |transports| may be non-null only if it's nonempty and |message| has no
@@ skipping 13 matching lines @@
   mutable util::Mutex mutex_;
   std::unique_ptr<MessagePipeEndpoint> endpoints_[2] MOJO_GUARDED_BY(mutex_);
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(MessagePipe);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_MESSAGE_PIPE_H_