[Payment Request] window.PaymentRequest must be undefined if PR is disabled

ios/chrome/browser/web/chrome_web_client.mm

 // Copyright 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"
 
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/ios/ios_util.h"
 #include "base/mac/bundle_locations.h"
@@ skipping 145 matching lines @@
   additional_schemes->push_back(dom_distiller::kDomDistillerScheme);
 }
 
 void ChromeWebClient::PostBrowserURLRewriterCreation(
     web::BrowserURLRewriter* rewriter) {
   rewriter->AddURLRewriter(&WillHandleWebBrowserAboutURL);
 }
 
 NSString* ChromeWebClient::GetEarlyPageScript(
     web::BrowserState* browser_state) const {
-  return GetPageScript(@"chrome_bundle");
+  NSString* chromePageScript = GetPageScript(@"chrome_bundle");

[Eugene But (OOO till 7-30), 2017/06/19 14:53:58]

s/chromePageScript/chrome_page_script

[Moe, 2017/06/19 15:11:10]

done.

+
+  if (!experimental_flags::IsPaymentRequestEnabled())
+    return chromePageScript;
+
+  NSString* kScriptTemplate = @"%@; %@";
+  return [NSString stringWithFormat:kScriptTemplate,
+                                    GetPageScript(@"payment_request"),
+                                    chromePageScript];
 }
 
 void ChromeWebClient::AllowCertificateError(
     web::WebState* web_state,
     int cert_error,
     const net::SSLInfo& info,
     const GURL& request_url,
     bool overridable,
     const base::Callback<void(bool)>& callback) {
   IOSSSLErrorHandler::HandleSSLError(web_state, cert_error, info, request_url,
                                      overridable, callback);
 }
 
 std::unique_ptr<base::TaskScheduler::InitParams>
 ChromeWebClient::GetTaskSchedulerInitParams() {
   return task_scheduler_util::GetBrowserTaskSchedulerInitParamsFromVariations();
 }
 
 void ChromeWebClient::PerformExperimentalTaskSchedulerRedirections() {
   task_scheduler_util::MaybePerformBrowserTaskSchedulerRedirection();
 }