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

ios/chrome/browser/web/BUILD.gn

 # Copyright 2016 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.
 
 import("//ios/web/js_compile.gni")
 
 source_set("web") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "dom_altering_lock.h",
@@ skipping 180 matching lines @@
     "error_page_generator_unittest.mm",
     "external_app_launcher_unittest.mm",
   ]
   deps = [
     ":test_support",
     ":web_internal",
     "//base",
     "//base/test:test_support",
     "//components/content_settings/core/browser",
     "//components/infobars/core",
+    "//components/payments/core",
     "//ios/chrome/browser",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/content_settings:content_settings",
     "//ios/chrome/browser/find_in_page",
     "//ios/chrome/browser/infobars",
     "//ios/chrome/browser/ui",
     "//ios/web",
     "//ios/web/public/test",
     "//ios/web/public/test/fakes",
     "//net",
@@ skipping 61 matching lines @@
   ]
   deps = [
     "//base",
     "//ios/chrome/test/base:perf_test_support",
     "//ios/web",
     "//ios/web/public/test",
     "//ios/web/public/test/fakes",
   ]
   libs = [ "WebKit.framework" ]
 }