Initial element hiding functionality

includes/include.preload.js

Index: includes/include.preload.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/includes/include.preload.js
@@ -0,0 +1,72 @@
+/*
+ * This Source Code is subject to the terms of the Mozilla Public License
+ * version 2.0 (the "License"). You can obtain a copy of the License at
+ * http://mozilla.org/MPL/2.0/.
+ */
+
+// ==UserScript==
+// @include *
+// ==/UserScript==
+
+var SELECTOR_GROUP_SIZE = 20;
+
+var elemhideElt = null;
+
+// Sets the currently used CSS rules for elemhide filters
+function setElemhideCSSRules(selectors)
+{
+  if (elemhideElt && elemhideElt.parentNode)
+    elemhideElt.parentNode.removeChild(elemhideElt);
+
+  if (!selectors)
+    return;
+
+  elemhideElt = document.createElement("style");
+  elemhideElt.setAttribute("type", "text/css");
+  document.documentElement.appendChild(elemhideElt);
+
+  var elt = elemhideElt;  // Use a local variable to avoid racing conditions
+  function setRules()
+  {
+    if (!elt.sheet)
+    {
+      // Stylesheet didn't initialize yet, wait a little longer
+      window.setTimeout(setRules, 0);
+      return;
+    }
+
+    // WebKit apparently chokes when the selector list in a CSS rule is huge.
+    // So we split the elemhide selectors into groups.
+    for (var i = 0, j = 0; i < selectors.length; i += SELECTOR_GROUP_SIZE, j++)
+    {
+      var selector = selectors.slice(i, i + SELECTOR_GROUP_SIZE).join(", ");
+      elt.sheet.insertRule(selector + " { display: none !important; }", j);
+    }
+  }
+  setRules();
+}
+
+function sendRequests()

[Felix Dahlke, 2012/10/10 14:21:42]

I'm only reviewing past this point, since everything above seems to be identical
to what we have in Chrome.

+{
+  // Make sure this is really an HTML page
+  if (!(document.documentElement instanceof window.HTMLElement))
+    return;
+
+  opera.extension.addEventListener("message", function(event)
+  {
+    var request = event.data;
+    switch (request.reqtype)

[Felix Dahlke, 2012/10/10 14:21:42]

I'd prefer an if to this switch, since there's only one case.

+    {
+      case "get-settings-response":
+        setElemhideCSSRules(request.selectors);
+        break;
+    }
+  }, false);
+  opera.extension.postMessage({reqtype: "get-settings", frameUrl: window.location.href});
+}
+
+// Document might not be initialized yet
+if (document.documentElement)
+  sendRequests();
+else
+  window.setTimeout(sendRequests, 0);