extension now enthusiastically alerts you when you visit the google dot com

extension/js/background.js

+var debug = 0;
+var stop_url = "https://www.google.com/"
+
 chrome.tabs.onUpdated.addListener(function (tabID, changeInfo, tab) {
+	var url;
+
+	chrome.tabs.query({'active': true, 'lastFocusedWindow': true}, function (tabs) {
+    	url = tabs[0].url;
+	if (debug){ console.log(url);}
+
 	if (changeInfo.status=='complete'){
-    		chrome.tabs.sendMessage(tab.id, { action: 'saySomething' });
-	}
-});
+		if (url==stop_url){
+    			chrome.tabs.sendMessage(tab.id, { action: 'saySomething' });
+			if (debug) {console.log("background something");}} } 
+});});

extension/js/content.js

 chrome.runtime.onMessage.addListener(function (msg) {
     /* We received a message, let's do as instructed */
     if (msg.action == 'saySomething') {
-        window.alert('something');
+        window.alert('Google!');
     }
 });