Add usage display support for Extension IME.

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": [
       {
@@ skipping 232 matching lines @@
               "candidates": {
                 "description": "List of candidates to show in the candidate window",
                 "type": "array",
                 "items": {
                   "type": "object",
                   "properties": {
                     "candidate": {"type": "string", "description": "The candidate"},
                     "id": {"type": "integer", "description": "The candidate's id"},
                     "parentId": {"type": "integer", "optional": true, "description": "The id to add these candidates under"},
                     "label": {"type": "string", "optional": true, "description": "Short string displayed to next to the candidate, often the shortcut key or index"},
-                    "annotation": {"type": "string", "optional": true, "description": "Additional text describing the candidate"}
+                    "annotation": {"type": "string", "optional": true, "description": "Additional text describing the candidate"},
+                    "usage": {
+                      "type": "object",
+                      "optional": true,
+                      "description": "The usage or detail description of word.",
+                      "properties": {
+                        "title": { "type": "string", "description": "The title string of details description."},
+                        "body": { "type": "string", "description": "The body string of detail description."}
+                      }
+                    }
                   }
                 }
               }
             }
           },
           {
             "type": "function",
             "name": "callback",
             "optional": true,
             "description": "Called when the operation completes.",
@@ skipping 264 matching lines @@
           {
             "type": "string",
             "name": "name",
             "description": "Name of the MenuItem which was activated"
           }
         ]
       }
     ]
   }
 ]