Add comment about lock_ in MidiManager::AccumulateMidiBytesSent

media/midi/midi_manager.cc

Index: media/midi/midi_manager.cc
diff --git a/media/midi/midi_manager.cc b/media/midi/midi_manager.cc
index 5fe9f2139f0ff3d325b53a3478cec4b3caad3488..c5ec6559b3cf33c5e940c894a6401bc7c6f7d764 100644
--- a/media/midi/midi_manager.cc
+++ b/media/midi/midi_manager.cc
@@ -153,6 +153,11 @@ void MidiManager::AccumulateMidiBytesSent(MidiManagerClient* client, size_t n) {
   if (clients_.find(client) == clients_.end())
     return;
 
+  // Continue to hold lock_ here in case another thread is currently doing
+  // EndSession.
+  // Note that if we are in EndSession, then a destructor is being called and
+  // it isn't really safe to call this method. But we don't have another way to
+  // check this right now.
   client->AccumulateMidiBytesSent(n);
 }