Make SkyDemo.apk start offline

Offline support isn't complete, but after this CL, SkyDemo.apk is able to start
and show some UI offline.

R=eseidel@chromium.org, eseidel@google.com

Review URL: https://codereview.chromium.org/1225883002.

engine/src/flutter/BUILD.gn

@@ -30,10 +30,7 @@ group("sky_apk") {
   ]
 
   if (is_android) {
-    deps += [
-      "//sky/apk/demo",
-      "//sky/services/intents",
-    ]
+    deps += [ "//sky/services/intents" ]
   }
 
   if (is_linux) {

engine/src/flutter/build/sky_app.gni

@@ -0,0 +1,57 @@
+# 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("//build/config/android/rules.gni")
+import("//sky/build/skyx.gni")
+
+template("sky_app") {
+  skyx("app") {
+    main_dart = invoker.main_dart
+
+    if (defined(invoker.manifest)) {
+      manifest = invoker.manifest
+    }
+
+    if (defined(invoker.sources)) {
+      sources = invoker.sources
+    }
+  }
+
+  copy_ex("assets") {
+    clear_dir = true
+    dest = "$target_gen_dir/assets"
+
+    sources = [
+      "$root_build_dir/icudtl.dat",
+    ]
+    deps = [
+      "//third_party/icu",
+    ]
+
+    if (enable_skyx) {
+      sources += [ "$target_gen_dir/app.skyx" ]
+      deps += [ ":app" ]
+    }
+  }
+
+  android_apk(target_name) {
+    apk_name = invoker.apk_name
+    android_manifest = "apk/AndroidManifest.xml"
+
+    native_libs = [ "libsky_shell.so" ]
+    asset_location = "$target_gen_dir/assets"
+
+    deps = [
+      "//base:base_java",
+      "//sky/shell:assets",
+      "//sky/shell:java",
+      "//sky/shell:sky_shell",
+      ":assets",
+    ]
+
+    if (defined(invoker.deps)) {
+      deps += invoker.deps
+    }
+  }
+}