[Payments] Add an entry for Payment Request to chrome://flags on iOS

ios/chrome/browser/web/chrome_web_client_unittest.mm

 // Copyright (c) 2014 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 "ios/chrome/browser/web/chrome_web_client.h"
 
 #import <UIKit/UIKit.h>
 
 #include <memory>
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/string_split.h"
 #include "base/strings/sys_string_conversions.h"
-#include "ios/chrome/browser/chrome_switches.h"
-#include "ios/chrome/browser/experimental_flags.h"
+#include "base/test/scoped_feature_list.h"
+#include "components/payments/core/features.h"
 #include "ios/web/public/test/fakes/test_browser_state.h"
 #import "ios/web/public/test/js_test_util.h"
 #include "ios/web/public/test/scoped_testing_web_client.h"
 #include "ios/web/public/test/web_test.h"
 #import "ios/web/public/web_view_creation_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/gtest_mac.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ skipping 67 matching lines @@
   web::TestBrowserState browser_state;
   WKWebView* web_view = web::BuildWKWebView(CGRectZero, &browser_state);
   web::ExecuteJavaScript(web_view, @"__gCrWeb = {};");
 
   web::ScopedTestingWebClient web_client(base::MakeUnique<ChromeWebClient>());
   NSString* script = web_client.Get()->GetEarlyPageScript(&browser_state);
   web::ExecuteJavaScript(web_view, script);
   EXPECT_NSEQ(@"undefined", web::ExecuteJavaScript(
                                 web_view, @"typeof window.PaymentRequest"));
 
-  base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
-      switches::kEnablePaymentRequest, std::string());
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(payments::features::kWebPayments);
   script = web_client.Get()->GetEarlyPageScript(&browser_state);
   web::ExecuteJavaScript(web_view, script);
   EXPECT_NSEQ(@"function", web::ExecuteJavaScript(
                                web_view, @"typeof window.PaymentRequest"));
 }
 
 }  // namespace