js_runtime: fix _JsonMap keys list type

[email protected]

Change-Id: Iec7d7e5229cb96e739e3d3bde73f5ce3534c5827
Reviewed-on: https://dart-review.googlesource.com/50020
Commit-Queue: Stephen Adams <[email protected]>
Reviewed-by: Stephen Adams <[email protected]>
Reviewed-by: Sigmund Cherem <[email protected]>

Author: rakudrama

sdk/lib/_internal/js_runtime/lib/convert_patch.dart

@@ -6,7 +6,7 @@
 
 import 'dart:_js_helper' show argumentErrorValue, patch;
 import 'dart:_foreign_helper' show JS;
-import 'dart:_interceptors' show JSExtendableArray;
+import 'dart:_interceptors' show JSArray, JSExtendableArray;
 import 'dart:_internal' show MappedIterable, ListIterable;
 import 'dart:collection' show LinkedHashMap, MapBase;
 import 'dart:_native_typed_data' show NativeUint8List;
@@ -274,7 +274,7 @@ class _JsonMap extends MapBase<String, dynamic> {
     assert(!_isUpgraded);
     List keys = _data;
     if (keys == null) {
-      keys = _data = _getPropertyNames(_original);
+      keys = _data = new JSArray<String>.typed(_getPropertyNames(_original));
     }
     return JS('JSExtendableArray', '#', keys);
   }

tests/corelib_2/corelib_2.status

@@ -227,7 +227,6 @@ iterable_followed_by_test: RuntimeError
 iterable_return_type_test/01: RuntimeError # Issue 20085
 iterable_return_type_test/02: RuntimeError # Dart2js does not support Uint64*.
 iterable_to_list_test/01: RuntimeError # Issue 26501
-json_map_test: RuntimeError
 list_concurrent_modify_test: RuntimeError # dart2js does not fully implement these
 list_test/01: RuntimeError
 list_test/none: RuntimeError
@@ -259,7 +258,6 @@ iterable_followed_by_test: RuntimeError
 iterable_return_type_test/01: RuntimeError # Issue 20085
 iterable_return_type_test/02: RuntimeError # Dart2js does not support Uint64*.
 iterable_to_list_test/01: RuntimeError # Issue 26501
-json_map_test: RuntimeError
 list_concurrent_modify_test: RuntimeError # dart2js does not fully implement these
 list_test/01: RuntimeError
 list_test/none: RuntimeError