Bug 1539265 - Add ::marker pseudo-element handling to WalkerIndex. r=jdescottes

So ::marker pseudo elements can be found via searching for "::marker" in the
markup view.

Differential Revision: https://phabricator.services.mozilla.com/D25109

--HG--
extra : moz-landing-system : lando

devtools/server/actors/utils/walker-search.js

@@ -93,7 +93,10 @@ WalkerIndex.prototype = {
         // For each element node, we get the tagname and all attributes names
         // and values
         const localName = node.localName;
-        if (localName === "_moz_generated_content_before") {
+        if (localName === "_moz_generated_content_marker") {
+          this._addToIndex("tag", node, "::marker");
+          this._addToIndex("text", node, node.textContent.trim());
+        } else if (localName === "_moz_generated_content_before") {
           this._addToIndex("tag", node, "::before");
           this._addToIndex("text", node, node.textContent.trim());
         } else if (localName === "_moz_generated_content_after") {