Removing interfaces from dart:html

lib/html/src/KeyLocation.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Defines the standard key locations returned by
  * KeyboardEvent.getKeyLocation.
  */
-interface KeyLocation {
+abstract class KeyLocation {
 
   /**
    * The event key is not distinguished as the left or right version
    * of the key, and did not originate from the numeric keypad (or did not
    * originate with a virtual key corresponding to the numeric keypad).
    */
   static const int STANDARD = 0;
 
   /**
    * The event key is in the left key location.
@@ skipping 16 matching lines @@
    * keypad or a virtual keyboard.
    */
   static const int MOBILE = 4;
 
   /**
    * The event key originated on a game controller or a joystick on a mobile
    * device.
    */
   static const int JOYSTICK = 5;
 }