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

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index c247b45e1218723501cac192edca8f1e78820fe2..faf61db0aab3d5b891deaf1257fbbfe1bf6e18ab 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1730,6 +1730,9 @@ const FeatureEntry kFeatureEntries[] = {
      IDS_FLAGS_MERGE_KEY_CHAR_EVENTS_DESCRIPTION, kOsWin,
      ENABLE_DISABLE_VALUE_TYPE(switches::kEnableMergeKeyCharEvents,
                                switches::kDisableMergeKeyCharEvents)},
+    {"use-winrt-midi-api", IDS_FLAGS_USE_WINRT_MIDI_API_NAME,
+     IDS_FLAGS_USE_WINRT_MIDI_API_DESCRIPTION, kOsWin,
+     SINGLE_VALUE_TYPE(switches::kUseWinrtMidiApi)},
 #endif  // defined(OS_WIN)
 #if BUILDFLAG(ENABLE_BACKGROUND)
     {"enable-push-api-background-mode", IDS_FLAGS_PUSH_API_BACKGROUND_MODE_NAME,