wrap_jso should wrap JsArray as well, not always call wrap on its contents

tests/html/wrapping_collections_test.dart

+library wrapping_collection_test;
+
+import 'dart:html';
+import 'dart:js' as js;
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+
+/// Test that if we access objects through JS-interop we get the
+/// appropriate objects, even if dart:html maps them.
+main() {
+  test("Access through JS-interop", () {
+    var performance = js.context['performance'];
+    var entries = performance.callMethod('getEntries', const []);
+    entries.forEach((x) {
+        expect(x is js.JsObject, isTrue);
+    });
+  });
+
+  test("Access through dart:html", () {
+    var dartPerformance = wrap_jso(js.context['performance']);
+    var dartEntries = dartPerformance.getEntries();
+    dartEntries.forEach((x) {
+        expect(x is PerformanceEntry, isTrue);
+    });
+  });
+}