Fix the issue that wallpaper changes twice when both "onChanged" and "onAlarm" are fired.

chrome/test/data/chromeos/wallpaper_manager/unit_tests/api_mock.js

Index: chrome/test/data/chromeos/wallpaper_manager/unit_tests/api_mock.js
diff --git a/chrome/test/data/chromeos/wallpaper_manager/unit_tests/api_mock.js b/chrome/test/data/chromeos/wallpaper_manager/unit_tests/api_mock.js
index 74d6795e4996b618267e6e2910aa62cb31177b81..143e6c339ec091a389481bedc6dc57bb3564f669 100644
--- a/chrome/test/data/chromeos/wallpaper_manager/unit_tests/api_mock.js
+++ b/chrome/test/data/chromeos/wallpaper_manager/unit_tests/api_mock.js
@@ -215,6 +215,15 @@ var chrome = {
     },
     sync: {
       get: function(key, callback) {
+        var items = {};
+        switch (key) {
+          case Constants.AccessSurpriseMeEnabledKey:
+            items[Constants.AccessSurpriseMeEnabledKey] = true;
+          case Constants.AccessLastSurpriseWallpaperChangedDate:
+            items[Constants.AccessLastSurpriseWallpaperChangedDate] =
+                new Date().toDateString();
+        }
+        callback(items);
       },
       set: function(items, callback) {
       }