[Payment Request] Refactors the edit view controller

ios/chrome/browser/ui/payments/payment_request_edit_view_controller+internal.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 IOS_CHROME_BROWSER_UI_PAYMENTS_PAYMENT_REQUEST_EDIT_VIEW_CONTROLLER_INTERNAL_H_
 #define IOS_CHROME_BROWSER_UI_PAYMENTS_PAYMENT_REQUEST_EDIT_VIEW_CONTROLLER_INTERNAL_H_
 
 #import "ios/chrome/browser/ui/payments/payment_request_edit_view_controller.h"
 
 // Use these as the starting values for section identifier and item type enums
 // in subclasses. These values are chosen to prevent overlapping with the
 // section identifier and item type enums of this class.
 const NSInteger kSectionIdentifierEnumStart = kSectionIdentifierEnumZero + 20;
 const NSInteger kItemTypeEnumStart = kItemTypeEnumZero + 100;
 
 // Internal API for subclasses of PaymentRequestEditViewController.
 @interface PaymentRequestEditViewController (Internal)
 
 // Validates each field. If there is a validation error, displays an error
 // message item in the same section as the field and returns NO. Otherwise
 // removes the error message item in that section if one exists and sets the
 // value on the field. Returns YES if all the fields are validated successfully.
 - (BOOL)validateForm;
 
-// Called before the editor field items are added to the the collection view
-// model. Subclasses override this method to add items before the editor fields.
-- (void)loadHeaderItems;
-
 // Called after the editor field items have been added to the the collection
 // view model. Subclasses override this method to add items after the editor
 // fields.
 - (void)loadFooterItems;
 
 // Returns the index path for the cell associated with the currently focused
 // text field.
 - (NSIndexPath*)indexPathForCurrentTextField;
 
-// Adds an error message item in the section |sectionIdentifier| if
-// |errorMessage| is non-empty. Otherwise removes such an item if one exists.
-- (void)addOrRemoveErrorMessage:(NSString*)errorMessage
-        inSectionWithIdentifier:(NSInteger)sectionIdentifier;
-
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_PAYMENTS_PAYMENT_REQUEST_EDIT_VIEW_CONTROLLER_INTERNAL_H_