PaymentHandler: Initial implementation for PaymentInstruments.

third_party/WebKit/Source/modules/payments/PaymentInstrument.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-instrument
+
+dictionary PaymentInstrument {
+    required DOMString name;
+    // TODO(zino): PaymentInstrument should have icons attribute.
+    // The spec[1] defines it as a sequence of ImageObject but its definition
+    // is not clear yet.
+    // Please see: https://github.com/w3c/webpayments-payment-apps-api/issues/69
+    // sequence<ImageObject> icons;
+    sequence<DOMString> enabledMethods;
+    object capabilities;
+};