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

mojo/edk/system/message_pipe_endpoint.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_ENDPOINT_H_
 #define MOJO_EDK_SYSTEM_MESSAGE_PIPE_ENDPOINT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 54 matching lines @@
                                  uint32_t* num_handles,
                                  MojoReadMessageFlags flags);
   virtual HandleSignalsState GetHandleSignalsState() const;
   virtual MojoResult AddAwakable(Awakable* awakable,
                                  MojoHandleSignals signals,
                                  bool force,
                                  uint64_t context,
                                  HandleSignalsState* signals_state);
   virtual void RemoveAwakable(Awakable* awakable,
                               HandleSignalsState* signals_state);
+  virtual void RemoveAwakableWithContext(Awakable* awakable,
+                                         uint64_t context,
+                                         HandleSignalsState* signals_state);
 
   // Implementations must override these if they represent a proxy endpoint. An
   // implementation for a local endpoint needs not override these methods, since
   // they should never be called.
   virtual void Attach(ChannelEndpoint* channel_endpoint);
 
  protected:
   MessagePipeEndpoint() {}
 
  private:
   MOJO_DISALLOW_COPY_AND_ASSIGN(MessagePipeEndpoint);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_MESSAGE_PIPE_ENDPOINT_H_