Add text offset to OnSurroundingTextChanged

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",
     "description": "Use the <code>chrome.input.ime</code> API to implement a custom IME for Chrome OS. This allows your extension to handle keystrokes, set the composition, and manage the candidate window.",
     "types": [
       {
@@ skipping 683 matching lines @@
               "text": {
                 "type": "string",
                 "description": "The text around cursor."
               },
               "focus": {
                 "type": "integer",
                 "description": "The ending position of the selection. This value indicates caret position if there is no selection."
               },
               "anchor": {
                 "type": "integer",
-                "description": "The beginning position of the selection. This value indicates caret position if is no selection."
+                "description": "The beginning position of the selection. This value indicates caret position if there is no selection."
+              },
+              "offset": {
+                "type": "integer",
+                "description": "The offset position of the selection. This value indicates the number of characters not included in the surrounding text."

[Shu Chen, 2015/08/12 07:23:15]

Please describe clearly for the difference between offset and focus/anchor:
  focus/anchor is relative to the |text|, while offset is relative to the whole
text of the input field, which include the text isn't included in |text|.

[rsadam, 2015/08/12 21:46:52]

Done.

               }
             }
           }
         ]
       },
       {
         "name": "onReset",
         "type": "function",
         "description": "This event is sent when chrome terminates ongoing text input session.",
         "parameters": [
           {
             "type": "string",
             "name": "engineID",
             "description": "ID of the engine receiving the event"
           }
         ]
       }
     ]
   }
 ]