Removed |which| from KeyboardEvent and MouseEvent.

third_party/WebKit/Source/core/events/KeyboardEvent.idl

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 38 matching lines @@
                                                            [Default=Undefined] optional DOMString keyIdentifier,
                                                            [Default=Undefined] optional unsigned long location,
                                                            [Default=Undefined] optional boolean ctrlKey,
                                                            [Default=Undefined] optional boolean altKey,
                                                            [Default=Undefined] optional boolean shiftKey,
                                                            [Default=Undefined] optional boolean metaKey);
 
     // https://w3c.github.io/uievents/#KeyboardEvent-supplemental-interface
     readonly attribute long charCode;
     readonly attribute long keyCode;
-    readonly attribute long which;
 };