Issue 521 - Inject our stylesheet on per-site basis rather than globally

lib/child/elemHide.js

Index: lib/child/elemHide.js
===================================================================
--- a/lib/child/elemHide.js
+++ b/lib/child/elemHide.js
@@ -28,18 +28,21 @@ try
     delete proto.Components;
 }
 catch (e)
 {
   Cu.reportError(e);
 }
 
 let {XPCOMUtils} = Cu.import("resource://gre/modules/XPCOMUtils.jsm", {});
+let {Services} = Cu.import("resource://gre/modules/Services.jsm", {});
 
 let {shouldAllowAsync} = require("child/contentPolicy");
+let {getFrames, isPrivate} = require("child/utils");
+let {RequestNotifier} = require("child/requestNotifier");
 let {port} = require("messaging");
 let {Utils} = require("utils");
 
 // The allowXBL binding below won't have any effect on the element. For elements
 // that should be hidden however we don't return any binding at all, this makes
 // Gecko stop constructing the node - it cannot be shown.
 const allowXBL = "<bindings xmlns='http://www.mozilla.org/xbl'><binding id='dummy' bindToUntrustedContent='true'/></bindings>";
 const hideXBL = "<bindings xmlns='http://www.mozilla.org/xbl'/>";
@@ -288,8 +291,67 @@ HitRegistrationChannel.prototype = {
       let window = Utils.getRequestWindow(this);
       shouldAllowAsync(window, window.document, "ELEMHIDE", this.key, allow =>
       {
         resolve(allow ? allowXBL : hideXBL);
       });
     });
   }
 };
+
+let observer = {
+  QueryInterface: XPCOMUtils.generateQI([
+    Ci.nsIObserver, Ci.nsISupportsWeakReference
+  ]),
+
+  topic: "content-document-global-created",
+  styleURL: Utils.makeURI("about:abp-elemhide?css"),
+  sheet: null,
+
+  init: function()
+  {
+    Services.obs.addObserver(this, this.topic, true);
+    onShutdown.add(() =>
+    {
+      Services.obs.removeObserver(this, this.topic);
+    });
+
+    port.on("elemhideupdate", () =>
+    {
+      this.sheet = null;

[Thomas Greiner, 2016/06/23 14:12:42]

If I understand this correctly, we no longer apply changes in element hiding
rules right away but only after the page reloads. That'd be a regression to the
current behavior in Firefox (and probably also Element Hiding Helper) even
though that's how the extension currently behaves on other platforms.

If so, was this change intentional to make it more consistent with our other
versions or is this a performance optimization?

[Wladimir Palant, 2016/06/29 16:18:21]

Yes, this is very much desirable and indeed listed under "issues solved" in the
description of https://issues.adblockplus.org/ticket/521.

Element Hiding Helper will have to be adjusted slightly, I guess that ideally it
should make sure the styles for the current webpage get reapplied.

+    });
+  },
+
+  observe: function(subject, topic, data)
+  {
+    if (topic != this.topic)
+      return;
+
+    port.emitWithResponse("elemhideEnabled", {
+      frames: getFrames(subject),
+      isPrivate: isPrivate(subject)
+    }).then(({
+      enabled, contentType, docDomain, thirdParty, location, filter,
+      filterType
+    }) =>
+    {
+      if (enabled)
+      {
+        if (!this.sheet)
+        {
+          this.sheet = Utils.styleService.preloadSheet(this.styleURL,
+              Ci.nsIStyleSheetService.USER_SHEET);
+        }
+
+        let utils = subject.QueryInterface(Ci.nsIInterfaceRequestor)
+                           .getInterface(Ci.nsIDOMWindowUtils);
+        utils.addSheet(this.sheet, Ci.nsIStyleSheetService.USER_SHEET);
+      }
+      else if (filter)
+      {
+        RequestNotifier.addNodeData(subject.document, subject.top, {
+          contentType, docDomain, thirdParty, location, filter, filterType
+        });
+      }
+    });
+  }
+};
+observer.init();