Add tabs.onReplaced event to notify listeners of tabs being swapped due to prerendering or instant.

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 900 matching lines @@
           {"type": "integer", "name": "tabId", "minimum": 0},
           {
             "type": "object",
             "name": "removeInfo",
             "properties": {
               "windowId": {"type": "integer", "minimum": 0, "description": "the window whose tab is closed." },
               "isWindowClosing": {"type": "boolean", "description": "True when the tab is being closed because its window is being closed." }
             }
           }
         ]
+      },
+      {
+        "name": "onSwapped",

[Matt Perry, 2012/12/18 18:04:02]

nit: I have a slight preference for onReplaced.

[justinlin, 2012/12/19 23:42:42]

Done. Yea, sounds better.

+        "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}
+        ]
       }
     ]
   }
 ]