Trigger a tab updated event if the favicon URL changes.

chrome/common/extensions/api/tabs.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": "tabs",
     "dependencies": [ "extension", "windows" ],
     "types": [
       {
@@ skipping 704 matching lines @@
               },
               "url": {
                 "type": "string",
                 "optional": true,
                 "description": "The tab's URL if it has changed."
               },
               "pinned": {
                 "type": "boolean",
                 "optional": true,
                 "description": "The tab's new pinned state."
+              },
+              "favIconUrl": {
+                "type": "string",
+                "optional": true,
+                "description": "The tab's new favicon URL."
               }
             }
           },
           {
             "$ref": "Tab",
             "name": "tab",
             "description": "Gives the state of the tab that was updated."
           }
         ]
       },
@@ skipping 189 matching lines @@
         "type": "function",
         "description": "Fired when a tab is replaced with another tab due to prerendering or instant.",
         "parameters": [
           {"type": "integer", "name": "addedTabId", "minimum": 0},
           {"type": "integer", "name": "removedTabId", "minimum": 0}
         ]
       }
     ]
   }
 ]