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

mojo/edk/system/message_pipe_dispatcher.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_DISPATCHER_H_
 #define MOJO_EDK_SYSTEM_MESSAGE_PIPE_DISPATCHER_H_
 
 #include "mojo/edk/system/dispatcher.h"
 #include "mojo/edk/system/memory.h"
 #include "mojo/edk/util/ref_ptr.h"
@@ skipping 85 matching lines @@
                                    uint32_t* num_handles,
                                    MojoReadMessageFlags flags) override;
   HandleSignalsState GetHandleSignalsStateImplNoLock() const override;
   MojoResult AddAwakableImplNoLock(Awakable* awakable,
                                    MojoHandleSignals signals,
                                    bool force,
                                    uint64_t context,
                                    HandleSignalsState* signals_state) override;
   void RemoveAwakableImplNoLock(Awakable* awakable,
                                 HandleSignalsState* signals_state) override;
+  void RemoveAwakableWithContextImplNoLock(
+      Awakable* awakable,
+      uint64_t context,
+      HandleSignalsState* signals_state) override;
   void StartSerializeImplNoLock(Channel* channel,
                                 size_t* max_size,
                                 size_t* max_platform_handles) override
       MOJO_NOT_THREAD_SAFE;
   bool EndSerializeAndCloseImplNoLock(
       Channel* channel,
       void* destination,
       size_t* actual_size,
       std::vector<platform::ScopedPlatformHandle>* platform_handles) override
       MOJO_NOT_THREAD_SAFE;
 
   // This will be null if closed.
   util::RefPtr<MessagePipe> message_pipe_ MOJO_GUARDED_BY(mutex());
   unsigned port_ MOJO_GUARDED_BY(mutex());
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(MessagePipeDispatcher);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_MESSAGE_PIPE_DISPATCHER_H_