Implement midi permissions on top of the new common permission classes

content/renderer/media/midi_dispatcher.cc

Index: content/renderer/media/midi_dispatcher.cc
diff --git a/content/renderer/media/midi_dispatcher.cc b/content/renderer/media/midi_dispatcher.cc
index cbbd876332b963b614c394b0dcf8b57c9d1e144f..84d10f7fc3e37b3776b1797016d0bb9a36306d30 100644
--- a/content/renderer/media/midi_dispatcher.cc
+++ b/content/renderer/media/midi_dispatcher.cc
@@ -50,7 +50,8 @@ void MidiDispatcher::cancelSysexPermissionRequest(
       base::string16 origin = request.securityOrigin().toString();
       Send(new MidiHostMsg_CancelSysExPermissionRequest(
           routing_id(), it.GetCurrentKey(), GURL(origin)));
-      requests_.Remove(it.GetCurrentKey());
+      // The request will be removed by OnSysExPermissionApproved once
+      // the blink MIDIAccessInitializer object is deleted.
       break;
     }
   }