Bug 1612951 - Replace the usages of nsIDocShellTreeItem with BrowsingContext in about:performance. r=florian

`nsIDocShellTreeItem.rootTreeItem` has been deprecated.
We should use an approach based on BrowsingContext.

Differential Revision: https://phabricator.services.mozilla.com/D61496

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

toolkit/components/aboutperformance/content/aboutPerformance.js

@@ -690,7 +690,8 @@ var Control = {
       if (target.classList.contains("addon-icon")) {
         let row = target.parentNode.parentNode;
         let id = row.windowId;
-        let parentWin = window.docShell.rootTreeItem.domWindow;
+        let parentWin =
+          window.docShell.browsingContext.embedderElement.ownerGlobal;
         parentWin.BrowserOpenAddonsMgr(
           "addons://detail/" + encodeURIComponent(id)
         );