Add onChanged callback for chrome.sessions API.

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

Index: chrome/test/data/extensions/api_test/sessions/sessions.js
diff --git a/chrome/test/data/extensions/api_test/sessions/sessions.js b/chrome/test/data/extensions/api_test/sessions/sessions.js
index 431edbec72fb11ed0a052bebb3a721a68cc1e13f..31a9c570b2233d3a8563fedc2aa45ef2e9d1db7b 100644
--- a/chrome/test/data/extensions/api_test/sessions/sessions.js
+++ b/chrome/test/data/extensions/api_test/sessions/sessions.js
@@ -108,6 +108,16 @@ chrome.test.runTests([
   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(),
@@ -134,6 +144,16 @@ chrome.test.runTests([
   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(),