Convert the RSS extension to event pages to avoid a dedicated background process.

chrome/test/data/extensions/subscribe_page_action/background.js

 // Copyright (c) 2012 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.
 
-// A dictionary keyed off of tabId that keeps track of data per tab (for
-// example what feedUrl was detected in the tab).
-var feedData = {};
-
-chrome.extension.onRequest.addListener(function(request, sender) {
+chrome.extension.onMessage.addListener(function(request, sender) {
   if (request.msg == "feedIcon") {
     // First validate that all the URLs have the right schema.
     var input = [];
     for (var i = 0; i < request.feeds.length; ++i) {
       var a = document.createElement('a');
       a.href = request.feeds[i].href;
       if (a.protocol == "http:" || a.protocol == "https:") {
         input.push(request.feeds[i]);
       } else {
         console.log('Warning: feed source rejected (wrong protocol): ' +
                     request.feeds[i].href);
       }
     }
 
     if (input.length == 0)
       return;  // We've rejected all the input, so abort.
 
     // We have received a list of feed urls found on the page.
-    // Enable the page action icon.
-    feedData[sender.tab.id] = input;
-    chrome.pageAction.setTitle(
-      { tabId: sender.tab.id,
-        title: chrome.i18n.getMessage("rss_subscription_action_title")
-      });
-    chrome.pageAction.show(sender.tab.id);
+    var feeds = {};
+    feeds[sender.tab.id] = input;

[not at google - send to devlin, 2013/04/08 04:39:55]

initialize directly? var feeds = {...} (in fact you don't even really need to
declare a variable for it)

[Finnur, 2013/04/08 12:59:24]

This is actually the only way I could get it to work.

var feeds = {sender.tab.id: input};
 ... and ...
var feeds = {sender.tab.id.toString(): input};

gives me...

Uncaught SyntaxError: Unexpected token . 

Not a really helpful error message. I looked around for solutions and someone
suggested this and it worked like a charm.

[not at google - send to devlin, 2013/04/08 22:01:27]

Doh. I've been writing too much python.

+    chrome.storage.local.set(feeds, function() {
+      // Enable the page action icon.
+      chrome.pageAction.setTitle(
+        { tabId: sender.tab.id,
+          title: chrome.i18n.getMessage("rss_subscription_action_title")
+        });
+      chrome.pageAction.show(sender.tab.id);
+    });
   } else if (request.msg == "feedDocument") {
     // We received word from the content script that this document
     // is an RSS feed (not just a document linking to the feed).
     // So, we go straight to the subscribe page in a new tab and
     // navigate back on the current page (to get out of the xml page).
     // We don't want to navigate in-place because trying to go back
     // from the subscribe page takes us back to the xml page, which
     // will redirect to the subscribe page again (we don't support a
     // location.replace equivalant in the Tab navigation system).
     chrome.tabs.executeScript(sender.tab.id,
         { code: "if (history.length > 1) " +
                  "history.go(-1); else window.close();"
         });
     var url = "subscribe.html?" + encodeURIComponent(request.href);
     url = chrome.extension.getURL(url);
     chrome.tabs.create({ url: url, index: sender.tab.index });
   }
 });
 
 chrome.tabs.onRemoved.addListener(function(tabId) {
-  delete feedData[tabId];
+  chrome.storage.local.remove(tabId.toString());

[not at google - send to devlin, 2013/04/08 04:39:55]

I think (hope) the toString() is unnecessary.

[Finnur, 2013/04/08 12:59:24]

Nope, toString is needed. Otherwise I get:

Error in event handler for 'tabs.onRemoved': Invocation of form remove(integer)
doesn't match definition remove(string or array keys, optional function
callback) Error: Invocation of form remove(integer) doesn't match definition
remove(string or array keys, optional function callback)
    at normalizeArgumentsAndValidate (schemaUtils:120:11)
    at CustomBindingsObject.self.(anonymous function) [as remove]
(StorageArea:29:14)
    at chrome-extension://bmedchljhkolpfhojfonijnlhcdphapm/background.js:54:24
    at Event.dispatchToListener (event_bindings:356:21)
    at Event.dispatch_ (event_bindings:342:27)
    at dispatchArgs (event_bindings:214:26)
    at Object.chromeHidden.Event.dispatchEvent (event_bindings:223:7)
event_bindings:346

Overall I found the Storage API to be a lot more finicky than just localStorage.

[not at google - send to devlin, 2013/04/08 22:01:27]

Dang. Could you file bugs? I'm fixing the int key thing.

 });