PaymentApp: Initial implementation for PaymentAppManager.setManifest().

components/payments/payment_app.mojom

+// 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.
+
+module payments.mojom;
+
+enum PaymentAppManifestError {
+  NONE,
+  NOT_IMPLEMENTED,
+};
+
+struct PaymentAppOption {
+  string label;
+  string? icon;
+  string id;
+  array<string> enabled_methods;
+};
+
+struct PaymentAppManifest {
+  string label;
+  string? icon;
+  array<PaymentAppOption> options;
+};
+
+interface PaymentAppManager {
+  SetManifest(string service_worker_scope, PaymentAppManifest payment_app_manifest)
+      => (PaymentAppManifestError error);
+};