Warn web developer on missing favicon for PaymentRequest UI.

components/payments/mojom/payment_request.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.
 
 [JavaPackage="org.chromium.payments.mojom"]
 module payments.mojom;
 
 // The shipping address that the browser process provides to the renderer
 // process. Built either by the browser or a payment app.
 struct PaymentAddress {
@@ skipping 78 matching lines @@
 };
 
 interface PaymentRequestClient {
   OnShippingAddressChange(PaymentAddress address);
   OnShippingOptionChange(string shipping_option_id);
   OnPaymentResponse(PaymentResponse response);
   OnError(PaymentErrorReason error);
   OnComplete();
   OnAbort(bool aborted_successfully);
   OnCanMakePayment(CanMakePaymentQueryResult result);
+  WarnNoFavicon();
 };
 
 struct PaymentItem {
   string label;
   PaymentCurrencyAmount amount;
   bool pending;
 };
 
 struct PaymentShippingOption {
   string id;
@@ skipping 115 matching lines @@
   Init(PaymentRequestClient client,
        array<PaymentMethodData> method_data,
        PaymentDetails details,
        PaymentOptions options);
   Show();
   UpdateWith(PaymentDetails details);
   Abort();
   Complete(PaymentComplete result);
   CanMakePayment();
 };