Add "use-winrt-midi-api" flag to enable WinRT WebMIDI backend

media/midi/midi_manager_winrt.cc

Index: media/midi/midi_manager_winrt.cc
diff --git a/media/midi/midi_manager_winrt.cc b/media/midi/midi_manager_winrt.cc
index b8400e944a6404235e3a223bdd528adcbb756bc1..32b41e8933235dd5fb75a53db5a8dafc37987fc3 100644
--- a/media/midi/midi_manager_winrt.cc
+++ b/media/midi/midi_manager_winrt.cc
@@ -22,7 +22,6 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/timer/timer.h"
 #include "base/win/scoped_comptr.h"
-#include "base/win/windows_version.h"
 #include "media/midi/midi_scheduler.h"
 
 namespace media {
@@ -810,12 +809,6 @@ MidiManagerWinrt::~MidiManagerWinrt() {
 }
 
 void MidiManagerWinrt::StartInitialization() {
-  if (base::win::GetVersion() < base::win::VERSION_WIN10) {
-    VLOG(1) << "WinRT MIDI backend is only supported on Windows 10 or later.";
-    CompleteInitialization(Result::INITIALIZATION_ERROR);
-    return;
-  }
-
   com_thread_.init_com_with_mta(true);
   com_thread_.Start();
 
@@ -943,9 +936,5 @@ void MidiManagerWinrt::OnPortManagerReady() {
     CompleteInitialization(Result::OK);
 }
 
-MidiManager* MidiManager::Create() {
-  return new MidiManagerWinrt();
-}
-
 }  // namespace midi
 }  // namespace media