PaymentApp: Introduce PaymentAppDatabase class.

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 <utility>
+#include <vector>
+
+#include "base/callback_forward.h"
+
+namespace content {
+
+class PaymentAppContext {
+ public:
+  using GetAllManifestsCallback = base::Callback<void(

[please use gerrit instead, 2016/12/09 21:58:47]

Please add a comment about the meaning of this data type. A reader would have
hard time understanding what the int64_t is doing here.

[zino, 2016/12/09 22:30:16]

I agree with you.
So, I split it into subtypes and left a comment.

Done

+      const std::vector<
+          std::pair<int64_t, payments::mojom::PaymentAppManifestPtr>>&)>;
+  virtual void GetAllManifests(const GetAllManifestsCallback& callback) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_PAYMENT_APP_CONTEXT_H_