Web MIDI: fix multi-threading problem around message buffer handling

media/midi/midi_manager_mac.cc

Index: media/midi/midi_manager_mac.cc
diff --git a/media/midi/midi_manager_mac.cc b/media/midi/midi_manager_mac.cc
index 7bc8f2332e02f02fbd32342564fcf0eb933397b5..8b9a22333331ba0b8cb519f639422175f14b3894 100644
--- a/media/midi/midi_manager_mac.cc
+++ b/media/midi/midi_manager_mac.cc
@@ -147,10 +147,11 @@ void MIDIManagerMac::ReadMidi(MIDIEndpointRef source,
 }
 
 void MIDIManagerMac::SendMIDIData(MIDIManagerClient* client,
-                                  int port_index,
-                                  const uint8* data,
-                                  size_t length,
+                                  size_t port_index,
+                                  const std::vector<uint8>& data,
                                   double timestamp) {
+  DCHECK(CurrentlyOnMIDISendThread());
+
   // System Exclusive has already been filtered.
   MIDITimeStamp coremidi_timestamp = SecondsToMIDITimeStamp(timestamp);
 
@@ -159,14 +160,11 @@ void MIDIManagerMac::SendMIDIData(MIDIManagerClient* client,
       kMaxPacketListSize,
       midi_packet_,
       coremidi_timestamp,
-      length,
-      data);
+      data.size(),
+      &data[0]);
 
   // Lookup the destination based on the port index.
-  // TODO(crogers): re-factor |port_index| to use unsigned
-  // to avoid the need for this check.
-  if (port_index < 0 ||
-      static_cast<size_t>(port_index) >= destinations_.size())
+  if (port_index >= destinations_.size())
     return;
 
   MIDIEndpointRef destination = destinations_[port_index];
@@ -176,7 +174,7 @@ void MIDIManagerMac::SendMIDIData(MIDIManagerClient* client,
   // Re-initialize for next time.
   midi_packet_ = MIDIPacketListInit(packet_list_);
 
-  client->AccumulateMIDIBytesSent(length);
+  client->AccumulateMIDIBytesSent(data.size());
 }
 
 MIDIPortInfo MIDIManagerMac::GetPortInfoFromEndpoint(