The item that needs to be added to the array that is passed to the Menu.buildFromTemplate electron function. This gives you dev tools in a menu in the tray.

electron_app_menu_devtools.js

{
  label: 'View',
  submenu: [
    {
      label: 'Toggle Developer Tools',
      accelerator: (function() {
        if (process.platform == 'darwin')
          return 'Alt+Command+I';
        else
          return 'Ctrl+Shift+I';
      })(),
      click: function(item, focusedWindow) {
        if (focusedWindow)
          focusedWindow.webContents.toggleDevTools();
      }
    }
  ]
},