[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/edk/system/message_pipe_dispatcher.cc

 // Copyright 2015 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.
 
 #include "mojo/edk/system/message_pipe_dispatcher.h"
 
 #include <limits>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ skipping 621 matching lines @@
     rv.satisfiable_signals |= MOJO_HANDLE_SIGNAL_WRITABLE;
     rv.satisfiable_signals |= MOJO_HANDLE_SIGNAL_READABLE;
   } else {
     rv.satisfied_signals |= MOJO_HANDLE_SIGNAL_PEER_CLOSED;
   }
   rv.satisfiable_signals |= MOJO_HANDLE_SIGNAL_PEER_CLOSED;
   return rv;
 }
 
 void MessagePipeDispatcher::OnPortStatusChanged() {
-  RequestContext request_context;
+  DCHECK(RequestContext::current());
 
   base::AutoLock lock(signal_lock_);
 
   // We stop observing our port as soon as it's transferred, but this can race
   // with events which are raised right before that happens. This is fine to
   // ignore.
   if (port_transferred_)
     return;
 
 #if !defined(NDEBUG)
@@ skipping 15 matching lines @@
     DVLOG(1) << "Peer closure detected on message pipe " << pipe_id_
              << " endpoint " << endpoint_ << " [port=" << port_.name() << "]";
   }
 #endif
 
   awakables_.AwakeForStateChange(GetHandleSignalsStateNoLock());
 }
 
 }  // namespace edk
 }  // namespace mojo