PaymentApp: Factor out functions to serialize/deserialize manifest data.

content/public/browser/payment_app_context.h

+// Copyright 2016 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.
+
+#ifndef CONTENT_PUBLIC_BROWSER_PAYMENT_APP_CONTEXT_H_
+#define CONTENT_PUBLIC_BROWSER_PAYMENT_APP_CONTEXT_H_
+
+#include "base/callback_forward.h"
+
+namespace content {
+
+class PaymentAppContext {
+ public:
+  using PaymentAppManifestWithID = std::pair<int64_t, payments::mojom::PaymentAppManifestPtr>;
+  using GetAllManifestsCallback = base::Callback<void(
+      const std::vector<PaymentAppManifestWithID>&)>;
+  virtual void GetAllManifests(const GetAllManifestsCallback& callback) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_PAYMENT_APP_CONTEXT_H_