Issue 5090 - Use user stylesheets for element hiding if possible

background.js

Index: background.js
diff --git a/background.js b/background.js
index cb7a861be117f6a390b74ffa1370bb9de50ba33f..1ef27a2a2af6eff21491c1e782fc4d3e603d75da 100644
--- a/background.js
+++ b/background.js
@@ -21,9 +21,12 @@ const {RegExpFilter} = require("filterClasses");
 const {ElemHide} = require("elemHide");
 const {checkWhitelisted} = require("whitelisting");
 const {extractHostFromFrame} = require("url");
+const {hideElements} = require("css");
 const {port} = require("messaging");
 const devtools = require("devtools");
 
+let tryInsertCSS = true;
+
 port.on("get-selectors", (msg, sender) =>
 {
   let selectors;
@@ -45,7 +48,35 @@ port.on("get-selectors", (msg, sender) =>
     selectors = [];
   }
 
-  return {selectors, trace};
+  if (!tryInsertCSS)
+    return {selectors, trace, inject: true};
+
+  return new Promise(resolve =>
+  {
+    hideElements(sender.page.id, sender.frame.id, selectors, error =>
+    {
+      if (error && /\bError processing cssOrigin\b/.test(error.message) != -1)

[kzar, 2017/04/20 06:17:15]

From the discussion in the Chromium issue it seems like they expect us to just
check the user agent string to figure out if user stylesheets can be injected,
and the cssOrigin option won't be supported anyway.

So I wonder if we're better off just using the info module to check platform +
version in order to see if the feature is supported, rather than seeing if an
exception is thrown that matches this regexp?

We're just going to have to change the logic in the future otherwise. For
example we're going to have to check the platform and version here anyway and
we're going to have to at least check the platform in lib/css.js before passing
the cssOrigin option which Chrome doesn't like.

[Manish Jethani, 2017/04/20 12:50:32]

Yeah, this makes sense. I've added a userStylesheetsSupported property to the
css module now. The background page checks the value before trying to use the
hideElements function.

[kzar, 2017/04/21 11:20:22]

Nice, looks good. Could you update the issue description to match?

+        tryInsertCSS = false;
+
+      let response = {trace, inject: !!error};
+
+      if (trace || error)
+        response.selectors = selectors;
+
+      resolve(response);
+    });
+  });
+});
+
+port.on("hide-elements", (msg, sender) =>
+{
+  return new Promise(resolve =>
+  {
+    hideElements(sender.page.id, sender.frame.id, msg.selectors, error =>
+    {
+      resolve({success: !error});
+    });
+  });
 });
 
 port.on("forward", (msg, sender) =>