Web MIDI: adding backend to support dynamic instantiation on Windows

media/midi/midi_service.h

Index: media/midi/midi_service.h
diff --git a/media/midi/midi_service.h b/media/midi/midi_service.h
index 0428527cc1d7b20fd4f0fdab35297db4c0ad8905..722d5e6219a844fb4b20e70778bc41f37df17af1 100644
--- a/media/midi/midi_service.h
+++ b/media/midi/midi_service.h
@@ -20,8 +20,6 @@
 
 namespace midi {
 
-class MidiManagerAlsa;
-
 // Manages MidiManager backends.  This class expects to be constructed and
 // destructed on the browser main thread, but methods can be called on both
 // the main thread and the I/O thread.
@@ -49,9 +47,6 @@ class MIDI_EXPORT MidiService final {
                             const std::vector<uint8_t>& data,
                             double timestamp);
 
- private:
-  friend class MidiManagerAlsa;
-
   // Returns a SingleThreadTaskRunner reference to serve MidiManager. Each
   // TaskRunner will be constructed on demand.
   // MidiManager that supports the dynamic instantiation feature will use this
@@ -61,6 +56,7 @@ class MIDI_EXPORT MidiService final {
   // another MidiManager is instantiated.
   scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner(size_t runner_id);
 
+ private:
   // Holds MidiManager instance. If the dynamic instantiation feature is
   // enabled, the MidiManager would be constructed and destructed on the I/O
   // thread, and all MidiManager methods would be called on the I/O thread.