[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/edk/system/data_pipe_producer_dispatcher.cc

 // 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.
 
 #include "mojo/edk/system/data_pipe_producer_dispatcher.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <utility>
@@ skipping 455 matching lines @@
 void DataPipeProducerDispatcher::NotifyWrite(uint32_t num_bytes) {
   DVLOG(1) << "Data pipe producer " << pipe_id_ << " notifying peer: "
            << num_bytes << " bytes written. [control_port="
            << control_port_.name() << "]";
 
   SendDataPipeControlMessage(node_controller_, control_port_,
                              DataPipeCommand::DATA_WAS_WRITTEN, num_bytes);
 }
 
 void DataPipeProducerDispatcher::OnPortStatusChanged() {
-  // This has to be outside |lock_| because the watch callback can call data
-  // pipe functions which then try to acquire |lock_|.
-  RequestContext request_context;
+  DCHECK(RequestContext::current());
+
   base::AutoLock lock(lock_);
 
   // We stop observing the control port as soon it's transferred, but this can
   // race with events which are raised right before that happens. This is fine
   // to ignore.
   if (transferred_)
     return;
 
   DVLOG(1) << "Control port status changed for data pipe producer " << pipe_id_;
 
@@ skipping 51 matching lines @@
   }
 
   if (peer_closed_ != was_peer_closed ||
       available_capacity_ != previous_capacity) {
     awakable_list_.AwakeForStateChange(GetHandleSignalsStateNoLock());
   }
 }
 
 }  // namespace edk
 }  // namespace mojo