Dart: Adds a program to create snapshots of Mojo apps.

examples/dart/hello_world/hello/BUILD.gn

 # Copyright 2015 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.
 
 import("//mojo/public/dart/rules.gni")
 
-dartzip_packaged_application("hello") {
+dartzip_packaged_application("mojo_dart_hello_dartzip") {
+  output_name = "mojo_dart_hello"
   sources = [
     "main.dart",
   ]
   deps = [
     "//mojo/public/dart",
   ]
 }
+
+dart_pkg("mojo_dart_hello_pkg") {
+  entrypoints = [ "main.dart" ]
+  sources = [
+    "pubspec.yaml",
+  ]
+  deps = [
+    "//mojo/public/dart",
+  ]
+}
+
+group("hello") {
+  deps = [
+    ":mojo_dart_hello_dartzip",
+    ":mojo_dart_hello_pkg",
+  ]
+}