Fix another stupid bug in Gmail Checker on Chrome 21

chrome/common/extensions/docs/examples/extensions/gmail/background.js

Index: chrome/common/extensions/docs/examples/extensions/gmail/background.js
diff --git a/chrome/common/extensions/docs/examples/extensions/gmail/background.js b/chrome/common/extensions/docs/examples/extensions/gmail/background.js
index 898dbb5351d37987f303be24aa3a705305d59b34..8f26bfed9faab3bc64530d430f7eb307f087408e 100644
--- a/chrome/common/extensions/docs/examples/extensions/gmail/background.js
+++ b/chrome/common/extensions/docs/examples/extensions/gmail/background.js
@@ -289,7 +289,9 @@ function onInit() {
 
 function onAlarm(alarm) {
   console.log('Got alarm', alarm);
-  if (alarm.name == 'watchdog') {
+  // |alarm| can be undefined because onAlarm also gets called from
+  // window.setTimeout on old chrome versions.
+  if (alarm && alarm.name == 'watchdog') {
     onWatchdog();
   } else {
     startRequest({scheduleRequest:true, showLoadingAnimation:false});