chrome.settingsPrivate: Implement onPrefsChanged event handling.

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

Index: chrome/test/data/extensions/api_test/settings_private/test.js
diff --git a/chrome/test/data/extensions/api_test/settings_private/test.js b/chrome/test/data/extensions/api_test/settings_private/test.js
index 86104b15a50feeeaf2a78336feffc61e3ab4f8ac..28ac7f644ab45427c87e58512b6766ee265e1206 100644
--- a/chrome/test/data/extensions/api_test/settings_private/test.js
+++ b/chrome/test/data/extensions/api_test/settings_private/test.js
@@ -6,7 +6,8 @@
 // that callbacks are correctly invoked, expected parameters are correct,
 // and failures are detected.
 
-var kTestPrefName = 'test.foo_bar';
+var kTestPrefName = 'download.default_directory';
+var kTestPrefValue = '/Downloads';
 var kTestPageId = 'pageId';
 
 function callbackResult(result) {
@@ -20,7 +21,7 @@ var availableTests = [
   function setPref() {
     chrome.settingsPrivate.setPref(
         kTestPrefName,
-        true,
+        kTestPrefValue,
         kTestPageId,
         function(success) {
           callbackResult(success);
@@ -44,6 +45,21 @@ var availableTests = [
           chrome.test.succeed();
         });
   },
+  function onPrefsChanged() {
+    chrome.settingsPrivate.onPrefsChanged.addListener(function(prefs) {
+      chrome.test.assertTrue(prefs.length > 0);
+      chrome.test.assertEq(kTestPrefName, prefs[0].key);
+      chrome.test.assertEq(kTestPrefValue, prefs[0].value);
+      callbackResult(true);
+      chrome.test.succeed();
+    });
+
+    chrome.settingsPrivate.setPref(
+        kTestPrefName,
+        kTestPrefValue,
+        kTestPageId,
+        function() {});
+  },
 ];
 
 var testToRun = window.location.search.substring(1);