Introduce runtime.onSuspendCanceled() event.

chrome/common/extensions/api/runtime.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": "runtime",
     "documentation_permissions_required": ["runtime"],
     "properties": {
       "lastError": {
@@ skipping 99 matching lines @@
     ],
     "events": [
       {
         "name": "onInstalled",
         "type": "function",
         "description": "Fired when the extension is first installed."
       },
       {
         "name": "onSuspend",
         "type": "function",
-        "description": "Sent to the event page just before it is unloaded. This gives the extension opportunity to do some clean up. Note that since the page is unloading, any asynchronous operations started while handling this event are not guaranteed to complete."
+        "description": "Sent to the event page just before it is unloaded. This gives the extension opportunity to do some clean up. Note that since the page is unloading, any asynchronous operations started while handling this event are not guaranteed to complete. If more activity for the event page occurs before it gets unloaded the onSuspendCanceled event will be sent and the page won't be unloaded. "
+      },
+      {
+        "name": "onSuspendCanceled",
+        "type": "function",
+        "description": "Sent after onSuspend() to indicate that the app won't be unloaded after all."
       }
     ]
   }
 ]