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

media/midi/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//media/media_options.gni")
-import("//media/midi/midi_options.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   # For generate_jni().
   import("//build/config/android/rules.gni")
 }
 
 # Common configuration for targets in the media/midi directory.
 config("midi_config") {
   if (use_alsa && use_udev) {
@@ skipping 110 matching lines @@
 
   if (is_mac) {
     libs += [
       "CoreAudio.framework",
       "CoreFoundation.framework",
       "CoreMIDI.framework",
     ]
   }
 
   if (is_win) {
-    if (midi_use_winrt) {
-      sources += [
-        "midi_manager_winrt.cc",
-        "midi_manager_winrt.h",
-      ]
-    } else {
-      deps += [ "//device/usb" ]
-      sources += [
-        "midi_manager_win.cc",
-        "midi_manager_win.h",
-      ]
-    }
+    deps += [ "//device/usb" ]
+    sources += [
+      "midi_manager_win.cc",
+      "midi_manager_win.h",
+      "midi_manager_winrt.cc",
+      "midi_manager_winrt.h",
+    ]
   }
 
   if (use_alsa && use_udev) {
     deps += [
       "//crypto",
       "//crypto:platform",
     ]
     libs += [ "asound" ]
     sources += [
       "midi_manager_alsa.cc",
@@ skipping 40 matching lines @@
     sources += [ "midi_manager_alsa_unittest.cc" ]
   }
 
   if (use_x11) {
     deps += [ "//tools/xdisplaycheck" ]
   }
 
   # This target should not require the Chrome executable to run.
   assert_no_deps = [ "//chrome" ]
 }