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

ios/chrome/browser/payments/resources/payment_request_manager.js

 // 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.
 
 /**
  * @fileoverview JavaScript implementation of the Payment Request API. Conforms
  * to the 18 July 2016 editor's draft at
  * https://w3c.github.io/browser-payment-api/.
  *
  * This is a minimal implementation that sends data to the app side to present
  * the user interface. When loaded, installs the API onto the window object.
  */
 
 // Namespace for all PaymentRequest implementations. __gCrWeb must have already
 // been defined.
 __gCrWeb.paymentRequestManager = {
   /**
    * The pending PaymentRequest, if any. Used by the app side to invoke the
    * associated resolve or reject function.
    * @type {window.PaymentRequest}
    */
   pendingRequest: null,
 
   /**
    * The pending PaymentResponse, if any. Used by the app side to invoke the
-   * associated resolve or reject function.
+   * associated resolve function.
    * @type {window.PaymentResponse}
    */
   pendingResponse: null
 };
 __gCrWeb['paymentRequestManager'] = __gCrWeb.paymentRequestManager;
 
 /** @typedef {{
  *     methodData: !Array.<window.PaymentMethodData>,
  *     details: !window.PaymentDetails,
  *     options: (window.PaymentOptions|undefined)
@@ skipping 143 matching lines @@
     paymentResponse = window.PaymentResponse.parse(paymentResponseData);
   } catch (e) {
     throw new Error(
         "Internal PaymentRequest error: failed to parse PaymentResponse data.");
   }
   this.resolve_(paymentResponse);
 
   this.resolve_ = null;
   this.reject_ = null;
   __gCrWeb['paymentRequestManager'].pendingRequest = null;
+  __gCrWeb['paymentRequestManager'].pendingResponse = paymentResponse;
 }
 
 /**
  * Rejects the pending Promise. Should only be called by the app-side logic.
  * @param {!string} message An error message explaining why the Promise is being
  *     rejected.
  */
 window.PaymentRequest.prototype.reject = function(message) {
   if (!this.reject_) {
     throw new Error("Internal PaymentRequest error: reject function missing.");
@@ skipping 117 matching lines @@
    */
   this.details = details;
 
   /**
    * The pending resolve function provided to the Promise returned by
    * complete().
    * @type {?function()}
    * @private
    */
   this.resolve_ = null;
-
-  /**
-   * The pending reject function provided to the Promise returned by complete().
-   * @type {?function(string)}
-   * @private
-   */
-  this.reject_ = null;
 };
 
 /**
  * Communicates the result of processing the payment.
  * @param {boolean} success Indicates whether processing succeeded.
  * @return {!Promise} A promise to notify the caller when the user interface has
  *     been closed.
  */
 window.PaymentResponse.prototype.complete = function(success) {
-  if (__gCrWeb['paymentRequestManager'].pendingResponse) {
-    throw new Error(
-        'Internal PaymentRequest error: A response is already pending.');
-  }
-  __gCrWeb['paymentRequestManager'].pendingResponse = this;
-
   var message = {
     'command': 'paymentRequest.responseComplete'
   };
   __gCrWeb.message.invokeOnHost(message);
 
   var self = this;
   return new Promise(function(resolve, reject) {
     self.resolve_ = resolve;
-    self.reject_ = reject;
+    // Any reject function provided is ignored because the spec includes no
+    // provision for rejecting the response promise. User agents are directed to
+    // always resolve the promise.
   });
 };
 
 /**
  * Resolves the pending Promise. Should only be called by the app-side logic.
  */
 window.PaymentResponse.prototype.resolve = function() {
+  // If the page has not yet provided a resolve function, do nothing. This can
+  // happen in the case where the UI times out while waiting for the page to
+  // call complete().
   if (!this.resolve_) {
-    throw new Error("Internal PaymentRequest error: resolve function missing.");
+    return;
   }
 
   this.resolve_();
 
   this.resolve_ = null;
-  this.reject_ = null;
   __gCrWeb['paymentRequestManager'].pendingResponse = null;
 }
 
-/**
- * Rejects the pending Promise. Should only be called by the app-side logic.
- * @param {!string} message An error message explaining why the Promise is being
- *     rejected.
- */
-window.PaymentResponse.prototype.reject = function(message) {
-  if (!this.reject_) {
-    throw new Error("Internal PaymentRequest error: reject function missing.");
-  }
-
-  this.reject_(message);
-
-  this.resolve_ = null;
-  this.reject_ = null;
-  __gCrWeb['paymentRequestManager'].pendingResponse = null;
-}
-
 /**
  * Parses |paymentResponseData| into a PaymentResponse object.
  * @param {!__gCrWeb.paymentRequestManager.SerializedPaymentResponse}
  *     paymentResponseData A simple object representation of a PaymentResponse.
  * @return {window.PaymentResponse} A PaymentResponse object.
  */
 window.PaymentResponse.parse = function(paymentResponseData) {
   return new window.PaymentResponse(paymentResponseData['methodName'],
                                     paymentResponseData['details']);
 };