Add a simple cookies sample.

chrome/common/extensions/docs/examples/api/cookies/background.html

+<script>
+
+chrome.cookies.onChanged.addListener(function(info) {
+  console.log("onChanged" + JSON.stringify(info));
+});
+
+function focusOrCreateTab(url) {
+  chrome.windows.getAll({"populate":true}, function(windows) {
+    var existing_tab = null;
+    for (var i in windows) {
+      var tabs = windows[i].tabs;
+      for (var j in tabs) {
+        var tab = tabs[j];
+        if (tab.url == url) {
+          existing_tab = tab;
+          break;
+        }
+      }
+    }
+    if (existing_tab) {
+      chrome.tabs.update(existing_tab.id, {"selected":true});
+    } else {
+      chrome.tabs.create({"url":url, "selected":true});
+    }
+  });
+}
+
+chrome.browserAction.onClicked.addListener(function(tab) {
+  var manager_url = chrome.extension.getURL("manager.html");
+  focusOrCreateTab(manager_url);
+});
+
+</script>