Add code attribute into onKeyEvent argument.

chrome/common/extensions/api/input_ime.json

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
   {
     "namespace": "input.ime",
     "platforms": ["chromeos"],
     "types": [
       {
         "id": "KeyboardEvent",
         "type": "object",
         "description": "See http://www.w3.org/TR/DOM-Level-3-Events/#events-KeyboardEvent",
         "properties": {
           "type": {"type": "string", "description": "One of keyup or keydown.", "enum": ["keyup", "keydown"]},
           "requestId": {"type": "string", "description": "The ID of the request."},
           "key": {"type": "string", "description": "Value of the key being pressed"},
+          "code": {"type": "string", "description": "Value of the physical key being pressed. The value is not affected by current keyboard layout or modifier state."},
           "altKey": {"type": "boolean", "optional": true, "description": "Whether or not the ALT key is pressed."},
           "ctrlKey": {"type": "boolean", "optional": true, "description": "Whether or not the CTRL key is pressed."},
           "shiftKey": {"type": "boolean", "optional": true, "description": "Whether or not the SHIFT key is pressed."}
         }
       },
       {
         "id": "InputContext",
         "type": "object",
         "description": "Describes an input Context",
         "properties": {
@@ skipping 521 matching lines @@
           {
             "type": "string",
             "name": "name",
             "description": "Name of the MenuItem which was activated"
           }
         ]
       }
     ]
   }
 ]