PaymentHandler: Initial implementation for PaymentInstruments.

third_party/WebKit/Source/modules/payments/PaymentInstruments.idl

+// Copyright 2017 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.
+
+// https://w3c.github.io/webpayments-payment-apps-api/#payment-instruments
+
+[
+    RuntimeEnabled=PaymentApp,
+    Exposed=ServiceWorker
+] interface PaymentInstruments {
+    [ImplementedAs=deleteInstrument] Promise<boolean> delete(DOMString instrumentKey);
+    Promise<PaymentInstrument> get(DOMString instrumentKey);
+    Promise<sequence<DOMString>> keys();
+    Promise<boolean> has(DOMString instrumentKey);
+    Promise<void> set(DOMString instrumentKey, PaymentInstrument details);
+};