[mojo-edk] Expose notification source to MojoWatch callbacks

mojo/edk/system/data_pipe_consumer_dispatcher.cc

Index: mojo/edk/system/data_pipe_consumer_dispatcher.cc
diff --git a/mojo/edk/system/data_pipe_consumer_dispatcher.cc b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
index 10a80694fadbfa37ae2dfd495c3c6aeecb08c6bf..f978f9498e99f921123eceabe6d2a20290d737ee 100644
--- a/mojo/edk/system/data_pipe_consumer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
@@ -495,9 +495,7 @@ void DataPipeConsumerDispatcher::NotifyRead(uint32_t num_bytes) {
 }
 
 void DataPipeConsumerDispatcher::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_);