Add sysexEnabled readonly attribute to MIDIAccess

public/web/WebMIDIClient.h

 /*
  * Copyright (C) 2013 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 21 matching lines @@
 #define WebMIDIClient_h
 
 namespace blink {
 class WebMIDIPermissionRequest;
 
 class WebMIDIClient {
 public:
     virtual ~WebMIDIClient() { }
 
     // Request a permission to use system exclusive messages. Called when MIDIOptions.sysex is true.
-    virtual void requestSysExPermission(const WebMIDIPermissionRequest&) = 0;
+    // FIXME: Make following new functions pure virtual once Chromium implements them.
+    virtual void requestSysexPermission(const WebMIDIPermissionRequest&) { };
     // Cancel the request since the requesting frame may be moving to a new page.
-    virtual void cancelSysExPermissionRequest(const WebMIDIPermissionRequest&) = 0;
+    virtual void cancelSysexPermissionRequest(const WebMIDIPermissionRequest&) { };
+
+    // FIXME: Remove following old functions once Chromium usess new functions.
+    virtual void requestSysExPermission(const WebMIDIPermissionRequest&) { };
+    virtual void cancelSysExPermissionRequest(const WebMIDIPermissionRequest&) { };
 };
 
 } // namespace blink
 
 #endif // WebMIDIClient_h