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

mojo/edk/system/simple_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_SIMPLE_DISPATCHER_H_
 #define MOJO_EDK_SYSTEM_SIMPLE_DISPATCHER_H_
 
 #include <list>
 
 #include "mojo/edk/system/awakable_list.h"
@@ skipping 19 matching lines @@
 
   // |Dispatcher| protected methods:
   void CancelAllStateNoLock() 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;
 
  private:
   AwakableList awakable_list_ MOJO_GUARDED_BY(mutex());
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(SimpleDispatcher);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_SIMPLE_DISPATCHER_H_