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

ios/chrome/browser/experimental_flags.mm

 // Copyright 2015 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.
 
 // This file can be empty. Its purpose is to contain the relatively short lived
 // definitions required for experimental flags.
 
 #include "ios/chrome/browser/experimental_flags.h"
 
 #include <dispatch/dispatch.h>
@@ skipping 154 matching lines @@
   std::string group_name =
       base::FieldTrialList::FindFullName("PasswordGeneration");
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(switches::kEnableIOSPasswordGeneration))
     return true;
   if (command_line->HasSwitch(switches::kDisableIOSPasswordGeneration))
     return false;
   return group_name != "Disabled";
 }
 
-bool IsPaymentRequestEnabled() {
-  // This call activates the field trial, if needed, so it must come before any
-  // early returns.
-  std::string group_name =
-      base::FieldTrialList::FindFullName("IOSPaymentRequest");
-
-  // Check if the experimental flag is forced on or off.
-  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
-  if (command_line->HasSwitch(switches::kEnablePaymentRequest)) {
-    return true;
-  } else if (command_line->HasSwitch(switches::kDisablePaymentRequest)) {
-    return false;
-  }
-
-  // Check if the Finch experiment is turned on.
-  return base::StartsWith(group_name, "Enabled",
-                          base::CompareCase::INSENSITIVE_ASCII);
-}
-
 bool IsPhysicalWebEnabled() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(switches::kEnableIOSPhysicalWeb)) {
     return true;
   } else if (command_line->HasSwitch(switches::kDisableIOSPhysicalWeb)) {
     return false;
   }
 
   // Check if the finch experiment is turned on
   std::string group_name =
@@ skipping 113 matching lines @@
   } else if (command_line->HasSwitch(
                  switches::kDisableThirdPartyKeyboardWorkaround)) {
     return false;
   }
 
   // Check if the Finch experiment is turned on.
   return base::FeatureList::IsEnabled(kEnableThirdPartyKeyboardWorkaround);
 }
 
 }  // namespace experimental_flags