Add appengine/gcloud/mustache dependencies.

pkg/gcloud/lib/http.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.
+
+/// Provides access to an authenticated HTTP client which can be used to access
+/// Google APIs.
+library gcloud.http;
+
+import 'package:http/http.dart' as http;
+
+import 'service_scope.dart' as ss;
+
+const Symbol _authenticatedClientKey = #_gcloud.http;
+
+/// Access the [http.Client] object available in the current service scope.
+///
+/// The returned object will be the one which was previously registered with
+/// [registerAuthClientService] within the current (or a parent) service
+/// scope.
+///
+/// Accessing this getter outside of a service scope will result in an error.
+/// See the `package:gcloud/service_scope.dart` library for more information.
+http.Client get authClientService => ss.lookup(_authenticatedClientKey);
+
+/// Registers the [http.Client] object within the current service scope.
+///
+/// The provided `client` object will be avilable via the top-level
+/// `authenticatedHttp` getter.
+///
+/// Calling this function outside of a service scope will result in an error.
+/// Calling this function more than once inside the same service scope is not
+/// allowed.
+void registerAuthClientService(http.Client client, {bool close: true}) {
+  ss.register(_authenticatedClientKey, client);
+  if (close) {
+    ss.registerScopeExitCallback(() => client.close());
+  }
+}