Add onChanged callback for chrome.sessions API.

chrome/common/extensions/api/sessions.json

 // Copyright 2013 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": "sessions",
     "description": "Use the <code>chrome.sessions</code> API to query and restore tabs and windows from a browsing session.",
     "types": [
       {
@@ skipping 89 matching lines @@
               {
                 "$ref": "Session",
                 "name": "restoredSession",
                 "description": "A $(ref:sessions.Session) containing the restored $(ref:windows.Window) or $(ref:tabs.Tab) object."
               }
             ]
           }
         ]
       }
     ],
+    "events": [

[not at google - send to devlin, 2014/03/17 14:21:18]

Cool, we've wanted to add this sort of functionality for a while.

We will probably want to include some data about the sessions which changed in
here.

However, I can't find a reference to a proposal for this API. Typically you
would fill out the API proposal on that page (it's a public document) explaining
the use case for this method and so on.

A number of the questions won't apply to you but the most important part is
proposing the new event.

[wjywbs, 2014/03/17 19:27:24]

Sure, I will write the proposal tonight.

[not at google - send to devlin, 2014/03/19 16:22:41]

Ok, let's resolve my comments in there. Then ping this CL to me again.

+      {
+        "name": "onRecentlyClosed",
+        "description": "Fired when recently closed tabs and/or windows are changed.",
+        "type": "function"
+      }
+    ],
     "properties": {
       "MAX_SESSION_RESULTS": {
         "value": 25,
         "description": "The maximum number of $(ref:sessions.Session) that will be included in a requested list."
       }
     }
   }
 ]