Introduce MIDIInputMap and MIDIOutputMap.

Source/modules/webmidi/MIDIInput.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 40 matching lines @@
 
     // |timeStamp| is a DOMHighResTimeStamp in the time coordinate system of performance.now().
     void didReceiveMIDIData(unsigned portIndex, const unsigned char* data, size_t length, double timeStamp);
 
     virtual void trace(Visitor*) OVERRIDE;
 
 private:
     MIDIInput(MIDIAccess*, const String& id, const String& manufacturer, const String& name, const String& version);
 };
 
-typedef HeapVector<Member<MIDIInput> > MIDIInputVector;
-
 } // namespace blink
 
 #endif // MIDIInput_h