Add a timeout if the page doesn't call complete() in a timely fashion.

ios/chrome/browser/payments/js_payment_request_manager.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_PAYMENTS_JS_PAYMENT_REQUEST_MANAGER_H_
 #define IOS_CHROME_BROWSER_PAYMENTS_JS_PAYMENT_REQUEST_MANAGER_H_
 
 #import "ios/web/public/web_state/js/crw_js_injection_manager.h"
 
 namespace web {
 class PaymentResponse;
 }
 
 // Injects the JavaScript that implements the Payment Request API and provides
 // an app-side interface for interacting with it.
 @interface JSPaymentRequestManager : CRWJSInjectionManager
 
+// Executes a JS noop function. This is used to work around an issue where the
+// JS event queue is blocked while presenting the Payment Request UI.
+- (void)executeNoop;
+
 // Resolves the JavaScript promise associated with the current PaymentRequest
 // with the a JSON serialization of |paymentResponse|. |completionHandler| will
 // be invoked after the operation has completed with YES if successful.
 - (void)resolveRequestPromise:(const web::PaymentResponse&)paymentResponse
             completionHandler:(void (^)(BOOL))completionHandler;
 
 // Rejects the JavaScript promise associated with the current PaymentRequest
 // with the supplied |errorMessage|. |completionHandler| will be invoked after
 // the operation has completed with YES if successful.
 - (void)rejectRequestPromise:(NSString*)errorMessage
            completionHandler:(void (^)(BOOL))completionHandler;
 
 // Resolves the JavaScript promise associated with the current PaymentResponse.
 // |completionHandler| will be invoked after the operation has completed with
 // YES if successful.
 - (void)resolveResponsePromise:(void (^)(BOOL))completionHandler;
 
-// Rejects the JavaScript promise associated with the current PaymentResponse
-// with the supplied |errorMessage|. |completionHandler| will be invoked after
-// the operation has completed with YES if successful.
-- (void)rejectResponsePromise:(NSString*)errorMessage
-            completionHandler:(void (^)(BOOL))completionHandler;
+// Note that there is no rejectResponsePromise method because the spec includes
+// no provision for rejecting the response promise. User agents are directed to
+// always resolve the promise.
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_PAYMENTS_JS_PAYMENT_REQUEST_MANAGER_H_