implementation of tab contextmenu focus fix that works with PR phosphorjs/phosphor#355

Author: telamonian

packages/docmanager-extension/src/index.ts

@@ -634,6 +634,7 @@ function addCommands(
   });
   app.contextMenu.addItem({
     command: CommandIDs.showInFileBrowser,
+    passDataset: true,
     selector: '[data-type="document-title"]',
     rank: 3
   });