Adding JSON example. (#1)

jsonexample/lib/utils.dart

@@ -0,0 +1,26 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+String prettyPrintList(Iterable iter) {
+  if (iter == null) return 'NULL';
+
+  final buff = StringBuffer();
+  var isFirst = true;
+
+  buff.write('[');
+
+  for (final val in iter) {
+    if (!isFirst) buff.write(', ');
+    isFirst = false;
+    if (val is String) {
+      buff.write('"$val"');
+    } else {
+      buff.write(val.toString());
+    }
+  }
+
+  buff.write(']');
+
+  return buff.toString();
+}