Add MineDigger.apk that works offline

sky/sdk/example/mine_digger/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/tools/bindings/mojom.gni")
+assert(is_android)
 
-mojom("bindings") {
-  sources = [
-    "intent_receiver.mojom",
-  ]
+import("//sky/apk/rules.gni")
+
+sky_app("mine_digger") {
+  apk_name = "MineDigger"
+  main_dart = "lib/main.dart"
 }