Add appengine/gcloud/mustache dependencies.

pkg/appengine/lib/src/appengine_context.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library appengine.appengine_context;
+
+import 'server/assets.dart';
+
+class AppengineContext {
+  final String applicationID;
+  final String partition;
+  final String version;
+  final String module;
+  final String instance;
+  final AssetsManager assets;
+
+  AppengineContext(String partition, this.applicationID, this.version,
+                   this.module, this.instance, Uri pubServeUrl)
+      : partition = partition,
+        assets = new AssetsManager(pubServeUrl, partition == 'dev');
+
+  bool get isDevelopmentEnvironment => partition == 'dev';
+
+  String get fullQualifiedApplicationId => '$partition~$applicationID';
+
+  String get backgroundTicket {
+    var majorVersion = version.split('_')[0];
+    var escapedApplicationID =
+       applicationID.replaceAll(':', '_').replaceAll('.', '_');
+
+    return '$escapedApplicationID/$module.$majorVersion.$instance';
+  }
+}