Small cleanup in content MessagePort watcher usage

content/common/message_port.h

 // Copyright 2017 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 CONTENT_COMMON_MESSAGE_PORT_H_
 #define CONTENT_COMMON_MESSAGE_PORT_H_
 
 #include <vector>
 
 #include "base/callback.h"
@@ skipping 82 matching lines @@
 
     ~State();
 
     void ArmWatcher();
     void OnHandleReady(MojoResult result);
 
     static void CallOnHandleReady(uintptr_t context,
                                   MojoResult result,
                                   MojoHandleSignalsState signals_state,
                                   MojoWatcherNotificationFlags flags);
-
-    uintptr_t context_;
   };
   mutable scoped_refptr<State> state_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_MESSAGE_PORT_H_