[Payments] Have an observer for canMakePayment, for testing.

chrome/browser/payments/payment_request_factory.cc

 // 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.
 
 #include "chrome/browser/payments/payment_request_factory.h"
 
 #include <memory>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "chrome/browser/payments/chrome_payment_request_delegate.h"
 #include "components/payments/content/payment_request_delegate.h"
 #include "components/payments/content/payment_request_web_contents_manager.h"
 #include "content/public/browser/web_contents.h"
 
 namespace payments {
 
 void CreatePaymentRequestForWebContents(
     content::WebContents* web_contents,
     mojo::InterfaceRequest<payments::mojom::PaymentRequest> request) {
   DCHECK(web_contents);
   PaymentRequestWebContentsManager::GetOrCreateForWebContents(web_contents)
-      ->CreatePaymentRequest(web_contents,
-                             base::MakeUnique<ChromePaymentRequestDelegate>(
-                                web_contents),
-                             std::move(request));
+      ->CreatePaymentRequest(
+          web_contents,
+          base::MakeUnique<ChromePaymentRequestDelegate>(web_contents),
+          std::move(request),
+          /*observer_for_testing=*/nullptr);
 }
 
 }  // namespace payments