Add onChanged callback for chrome.sessions API.

chrome/test/data/extensions/api_test/sessions/sessions.js

 // 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.
 
 var pages = [pageUrl('a'), pageUrl('b'), pageUrl('c')];
 var firstWindowTabIds = [];
 var recentlyClosedSecondWindowTabIds = [];
 var recentlyClosedTabIds = [];
 var recentlyClosedWindowIds = [];
 var windowIds = [];
@@ skipping 90 matching lines @@
             assertEq(callArgs.length + 1, win.length);
           })
         );
       }
     );
   },
 
   function retrieveClosedTabs() {
     // Check that the recently closed list contains what we expect
     // after removing tabs.
+    var expectedCallbackCount = 2, callbackCount = 0;

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

what does this actually test?

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

Lines 63-79 of this file describe that this retrieveClosedTabs function will
close 2 tabs, so chrome.sessions.onRecentlyClosed will be triggered twice.

+    var doneListening = chrome.test.listenForever(
+      chrome.sessions.onRecentlyClosed,
+      function() {
+        callbackCount++;
+        if (callbackCount == expectedCallbackCount)
+          doneListening();
+      }
+    );
+
     callForEach(
       chrome.tabs.remove,
       firstWindowTabIds.slice(0, 2).reverse(),
       function each() {
       },
       function done() {
         chrome.sessions.getRecentlyClosed(
           {maxResults: 2},
           callbackPass(function(entries) {
             var expectedEntries = [
               { tab: { url: pages[0] } },
               { tab: { url: pages[1] } }
             ];
             checkEntries(expectedEntries, entries);
             entries.forEach(function(entry) {
               recentlyClosedTabIds.push(entry.tab.sessionId);
             });
           })
         );
       }
     );
   },
 
   function retrieveClosedWindows() {
     // Check that the recently closed list contains what we expect
     // after removing windows.
+    var expectedCallbackCount = 2, callbackCount = 0;
+    var doneListening = chrome.test.listenForever(
+      chrome.sessions.onRecentlyClosed,
+      function() {
+        callbackCount++;
+        if (callbackCount == expectedCallbackCount)
+          doneListening();
+      }
+    );
+
     callForEach(
       chrome.windows.remove,
       windowIds.slice(1, 3).reverse(),
       function each() {
       },
       function done() {
         chrome.sessions.getRecentlyClosed(
           {maxResults: 2},
           callbackPass(function(entries) {
             var expectedEntries = [
@@ skipping 159 matching lines @@
           chrome.windows.getAll({"populate": true},
             callbackPass(function(win) {
               assertEq(windowCountBeforeRestore, win.length);
             })
           );
         })
       );
     }));
   }
 ]);