Add the RSS page action extension....

chrome/test/data/extensions/samples/subscribe_page_action/feed_finder.js

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+if (window == top) {
+  findFeeds();
+  window.addEventListener("focus", findFeeds);
+}
+
+function findFeeds() {
+  // Find all the RSS link elements.
+  var result = document.evaluate(
+      '//link[@rel="alternate"][contains(@type, "rss") or ' +
+      'contains(@type, "atom") or contains(@type, "rdf")]',
+      document, null, 0, null);
+
+  var feeds = [];
+  var item;
+  while (item = result.iterateNext())
+    feeds.push(item.href);
+
+  // Notify the extension of the feed URLs we found.
+  chrome.extension.connect().postMessage(feeds);
+}