Add experimental Support for DOM3 KeyboardEvent key value

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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 [
     Constructor(DOMString type, optional KeyboardEventInit eventInitDict)
 ] interface KeyboardEvent : UIEvent {
     const unsigned long DOM_KEY_LOCATION_STANDARD = 0x00;
     const unsigned long DOM_KEY_LOCATION_LEFT     = 0x01;
     const unsigned long DOM_KEY_LOCATION_RIGHT    = 0x02;
     const unsigned long DOM_KEY_LOCATION_NUMPAD   = 0x03;
 
     [RuntimeEnabled=KeyboardEventCode] readonly attribute DOMString     code;
+    [RuntimeEnabled=KeyboardEventKey] readonly attribute DOMString     key;

[Wez, 2015/03/04 23:00:25]

nit: Suggest lining up these two lines, for readability (i.e. aligning
"readonly", etc)

[Habib Virji, 2015/03/09 15:14:27]

Done.

     readonly attribute DOMString        keyIdentifier;
     readonly attribute unsigned long    location;
     [ImplementedAs=location, DeprecateAs=KeyboardEventKeyLocation] readonly attribute unsigned long keyLocation; // Deprecated.
     readonly attribute boolean          ctrlKey;
     readonly attribute boolean          shiftKey;
     readonly attribute boolean          altKey;
     readonly attribute boolean          metaKey;
     readonly attribute boolean          repeat;
 
     boolean getModifierState(DOMString keyArgument);
 
     // FIXME: this does not match the version in the DOM spec.
     void initKeyboardEvent([Default=Undefined] optional DOMString type,
                            [Default=Undefined] optional boolean canBubble,
                            [Default=Undefined] optional boolean cancelable,
                            [Default=Undefined] optional Window view,
                            [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);
 
     readonly attribute long charCode;
     readonly attribute long keyCode;
     readonly attribute long which;
 };