fix: guard against duplicate TouchBarItem IDs (#22272)

* feat: Add OtherItemsProxy touchbar item

* review!

* fix: guard against duplicate TouchBarItem IDs

* add spec

lib/browser/api/touch-bar.js

@@ -53,6 +53,7 @@ class TouchBar extends EventEmitter {
     }
 
     let hasOtherItemsProxy = false
+    const idSet = new Set()
     items.forEach((item) => {
       if (!(item instanceof TouchBarItem)) {
         throw new Error('Each item must be an instance of TouchBarItem')
@@ -65,6 +66,12 @@ class TouchBar extends EventEmitter {
           throw new Error('Must only have one OtherItemsProxy per TouchBar')
         }
       }
+
+      if (!idSet.has(item.id)) {
+        idSet.add(item.id)
+      } else {
+        throw new Error('Cannot add a single instance of TouchBarItem multiple times in a TouchBar')
+      }
     })
 
     // register in separate loop after all items are validated