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

content/browser/renderer_host/media/midi_host.h

Index: content/browser/renderer_host/media/midi_host.h
diff --git a/content/browser/renderer_host/media/midi_host.h b/content/browser/renderer_host/media/midi_host.h
index f6b2813264e51e0b570d4383702e764e3f394743..976bbe54e4daf851e5cb2522d4f4e762094d005b 100644
--- a/content/browser/renderer_host/media/midi_host.h
+++ b/content/browser/renderer_host/media/midi_host.h
@@ -5,6 +5,8 @@
 #ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_MIDI_HOST_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_MIDI_HOST_H_
 
+#include <vector>
+
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
@@ -43,7 +45,7 @@ class CONTENT_EXPORT MIDIHost
   void OnStartSession(int client_id);
 
   // Data to be sent to a MIDI output port.
-  void OnSendData(int port,
+  void OnSendData(unsigned int port,
                   const std::vector<uint8>& data,
                   double timestamp);