Web MIDI: Add a run-time flag in blink

Source/WebKit/chromium/public/WebRuntimeFeatures.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 157 matching lines @@
 
     WEBKIT_EXPORT static void enableWebPInAcceptHeader(bool);
     WEBKIT_EXPORT static bool isWebPInAcceptHeaderEnabled();
 
     WEBKIT_EXPORT static void enableDirectoryUpload(bool);
     WEBKIT_EXPORT static bool isDirectoryUploadEnabled();
 
     WEBKIT_EXPORT static void enableExperimentalWebSocket(bool);
     WEBKIT_EXPORT static bool isExperimentalWebSocketEnabled();
 
+    WEBKIT_EXPORT static void enableWebMIDI(bool);
+    WEBKIT_EXPORT static bool isWebMIDIEnabled();
+
 private:
     WebRuntimeFeatures();
 };
 
 } // namespace WebKit
 
 #endif