[Payment Request] Populates region field if region code/name is valid.

ios/chrome/browser/ui/payments/region_data_loader.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_REGION_DATA_LOADER_H_
 #define IOS_CHROME_BROWSER_UI_PAYMENTS_REGION_DATA_LOADER_H_
 
 #import <Foundation/Foundation.h>
 
 #include "base/macros.h"
 #include "components/autofill/core/browser/region_combobox_model.h"
 #include "ui/base/models/combobox_model_observer.h"
 
 namespace autofill {
 class RegionDataLoader;
 }  // namespace autofill
 
 namespace ui {
 class ComboboxModel;
 }  // namespace ui
 
 @protocol RegionDataLoaderConsumer
 
-- (void)regionDataLoaderDidSucceedWithRegions:(NSArray<NSString*>*)regions;
+// To be called with a map of region codes to region names when region data for
+// the given country code is loaded asynchronously.
+- (void)regionDataLoaderDidSucceedWithRegions:
+    (NSDictionary<NSString*, NSString*>*)regions;
 
 @end
 
 class RegionDataLoader : public ui::ComboboxModelObserver {
  public:
   explicit RegionDataLoader(id<RegionDataLoaderConsumer> consumer);
   ~RegionDataLoader() override;
 
   void LoadRegionData(const std::string& country_code,
                       autofill::RegionDataLoader* autofill_region_data_loader);
 
   // ui::ComboboxModelObserver
   void OnComboboxModelChanged(ui::ComboboxModel* model) override;
 
  private:
   __weak id<RegionDataLoaderConsumer> consumer_;
   autofill::RegionComboboxModel region_model_;
 
   DISALLOW_COPY_AND_ASSIGN(RegionDataLoader);
 };
 
 #endif  // IOS_CHROME_BROWSER_UI_PAYMENTS_REGION_DATA_LOADER_H_