Adding JSON example. (#1)

jsonexample/lib/dart_convert/converted_simple_object.dart

@@ -0,0 +1,40 @@
+// 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.
+
+class ConvertedSimpleObject {
+  const ConvertedSimpleObject({
+    this.aString,
+    this.anInt,
+    this.aDouble,
+    this.aListOfStrings,
+    this.aListOfInts,
+    this.aListOfDoubles,
+  });
+
+  final String aString;
+  final int anInt;
+  final double aDouble;
+  final List<String> aListOfStrings;
+  final List<int> aListOfInts;
+  final List<double> aListOfDoubles;
+
+  factory ConvertedSimpleObject.fromJson(Map<String, dynamic> json) {
+    if (json == null) return null;
+
+    return ConvertedSimpleObject(
+      aString: json['aString'],
+      anInt: json['anInt'],
+      aDouble: json['aDouble'],
+      aListOfStrings: json['aListOfStrings'] != null
+          ? List<String>.from(json['aListOfStrings'])
+          : null,
+      aListOfInts: json['aListOfInts'] != null
+          ? List<int>.from(json['aListOfInts'])
+          : null,
+      aListOfDoubles: json['aListOfDoubles'] != null
+          ? List<double>.from(json['aListOfDoubles'])
+          : null,
+    );
+  }
+}