PaymentRequest JS should be injected only if PaymentRequest is enabled.

ios/chrome/browser/payments/payment_request_manager.mm

 // 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/chrome/browser/payments/payment_request_manager.h"
 
 #include "base/ios/ios_util.h"
 #import "base/ios/weak_nsobject.h"
 #import "base/mac/bind_objc_block.h"
 #include "base/mac/foundation_util.h"
@@ skipping 185 matching lines @@
 
 - (void)disconnectWebState {
   if (_webState) {
     _paymentRequestJsManager.reset();
     _webStateObserver.reset();
     [self disableCurrentWebState];
   }
 }
 
 - (void)initializeWebViewForPaymentRequest {
-  DCHECK(_webStateEnabled);
+  if (_enabled) {
+    DCHECK(_webStateEnabled);
 
-  [_paymentRequestJsManager inject];
-  _isScriptInjected = YES;
+    [_paymentRequestJsManager inject];
+    _isScriptInjected = YES;
+  }
 }
 
 - (BOOL)handleScriptCommand:(const base::DictionaryValue&)JSONCommand {
   if (![self webStateContentIsSecureHTML]) {
     return NO;
   }
 
   std::string command;
   if (!JSONCommand.GetString("command", &command)) {
     DLOG(ERROR) << "RECEIVED BAD JSON - NO 'command' field";
@@ skipping 92 matching lines @@
     (web::PaymentResponse)paymentResponse {
   [_paymentRequestJsManager resolveRequestPromise:paymentResponse
                                 completionHandler:nil];
 }
 
 #pragma mark - CRWWebStateObserver methods
 
 - (void)webState:(web::WebState*)webState
     didCommitNavigationWithDetails:
         (const web::LoadCommittedDetails&)load_details {
+  [self dismissUI];
   _isScriptInjected = NO;
-  [self dismissUI];
+  [self enableCurrentWebState];
   [self initializeWebViewForPaymentRequest];
-  [self enableCurrentWebState];
 }
 
 @end