Web MIDI: add a new UMA entry for the final result code

media/midi/midi_manager_usb.h

Index: media/midi/midi_manager_usb.h
diff --git a/media/midi/midi_manager_usb.h b/media/midi/midi_manager_usb.h
index f5316bbed5eb3e0035e830de04b0cadbb184450b..a91e3a3e9422625c1cec8db0dd12bf6422a6db1d 100644
--- a/media/midi/midi_manager_usb.h
+++ b/media/midi/midi_manager_usb.h
@@ -70,7 +70,7 @@ class USB_MIDI_EXPORT MidiManagerUsb
   // will be canceled silently (i.e. |callback| will not be called).
   // The function is public just for unit tests. Do not call this function
   // outside code for testing.
-  void Initialize(base::Callback<void(MidiResult result)> callback);
+  void Initialize(base::Callback<void(Result result)> callback);
 
  private:
   void OnEnumerateDevicesDone(bool result, UsbMidiDevice::Devices* devices);
@@ -81,7 +81,7 @@ class USB_MIDI_EXPORT MidiManagerUsb
   ScopedVector<UsbMidiOutputStream> output_streams_;
   scoped_ptr<UsbMidiInputStream> input_stream_;
 
-  base::Callback<void(MidiResult result)> initialize_callback_;
+  base::Callback<void(Result result)> initialize_callback_;
 
   // A map from <endpoint_number, cable_number> to the index of input jacks.
   base::hash_map<std::pair<int, int>, size_t> input_jack_dictionary_;