Make it possible to remove an Awakable with a specific "context" from a Dispatcher.

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 90 matching lines @@
   HandleSignalsState GetHandleSignalsState(unsigned port) const;
   MojoResult AddAwakable(unsigned port,
                          Awakable* awakable,
                          MojoHandleSignals signals,
                          bool force,
                          uint64_t context,
                          HandleSignalsState* signals_state);
   void RemoveAwakable(unsigned port,
                       Awakable* awakable,
                       HandleSignalsState* signals_state);
+  void RemoveAwakableWithContext(unsigned port,
+                                 Awakable* awakable,
+                                 uint64_t context,
+                                 HandleSignalsState* signals_state);
   void StartSerialize(unsigned port,
                       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);
@@ skipping 29 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_