[Payments] Basic validation in the credit card editor.

components/payments/payment_request_delegate.h

 // 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.
 
 #ifndef COMPONENTS_PAYMENTS_PAYMENT_REQUEST_DELEGATE_H_
 #define COMPONENTS_PAYMENTS_PAYMENT_REQUEST_DELEGATE_H_
 
 namespace autofill {
 class PersonalDataManager;
 }
 
 namespace payments {
 
 class PaymentRequest;
 
 class PaymentRequestDelegate {
  public:
   virtual ~PaymentRequestDelegate() {}
 
   // Shows the Payment Request dialog for the given |request|.
   virtual void ShowDialog(PaymentRequest* request) = 0;
 
   // Closes the same dialog that was opened by this delegate. Must be safe to
   // call when the dialog is not showing.
   virtual void CloseDialog() = 0;
 
   // Gets the PersonalDataManager associated with this PaymentRequest flow.
+  // Cannot be null.
   virtual autofill::PersonalDataManager* GetPersonalDataManager() = 0;
 };
 
 }  // namespace payments
 
 #endif  // COMPONENTS_PAYMENTS_PAYMENT_REQUEST_DELEGATE_H_