Use native Pub/Sub library primitives.

common/gcloud/pubsub/scopes.go

Index: common/gcloud/pubsub/scopes.go
diff --git a/common/gcloud/pubsub/scopes.go b/common/gcloud/pubsub/scopes.go
new file mode 100644
index 0000000000000000000000000000000000000000..01059def77c2e9be31e71de57b6143b5b3971917
--- /dev/null
+++ b/common/gcloud/pubsub/scopes.go
@@ -0,0 +1,23 @@
+// 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.
+
+package pubsub
+
+import (
+	"google.golang.org/cloud/pubsub"
+)
+
+var (
+	// PublisherScopes is the set of OAuth2 scopes needed for a publisher to
+	// publish messages.
+	PublisherScopes = []string{
+		pubsub.ScopePubSub,
+	}
+
+	// SubscriberScopes is the set of OAuth2 scopes needed for a subscriber to
+	// pull and acknowledge messages.
+	SubscriberScopes = []string{
+		pubsub.ScopePubSub,
+	}
+)