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)
+        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) =>