LibWeb/IDB: Implement IDBIndex::count

Author: https://github.com/stelar7
Commit: 852323009f
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4727
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/shannonbooth

Libraries/LibWeb/IndexedDB/Internal/Algorithms.cpp

@@ -1453,10 +1453,16 @@ WebIDL::ExceptionOr<GC::Ref<IDBKeyRange>> convert_a_value_to_a_key_range(JS::Rea
 }
 
 // https://w3c.github.io/IndexedDB/#count-the-records-in-a-range
-JS::Value count_the_records_in_a_range(GC::Ref<ObjectStore> source, GC::Ref<IDBKeyRange> range)
+JS::Value count_the_records_in_a_range(RecordSource source, GC::Ref<IDBKeyRange> range)
 {
     // 1. Let count be the number of records, if any, in source’s list of records with key in range.
-    auto count = source->count_records_in_range(range);
+    auto count = source.visit(
+        [range](GC::Ref<ObjectStore> object_store) {
+            return object_store->count_records_in_range(range);
+        },
+        [range](GC::Ref<Index> index) {
+            return index->count_records_in_range(range);
+        });
 
     // 2. Return count.
     return JS::Value(count);