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

ios/chrome/browser/payments/payment_request_manager.mm

Index: ios/chrome/browser/payments/payment_request_manager.mm
diff --git a/ios/chrome/browser/payments/payment_request_manager.mm b/ios/chrome/browser/payments/payment_request_manager.mm
index 657183145f2098c5333df7c8a8daa4518e4d0ad9..5aa3e0634fb2cf3d10ee80063b3be89dddf333aa 100644
--- a/ios/chrome/browser/payments/payment_request_manager.mm
+++ b/ios/chrome/browser/payments/payment_request_manager.mm
@@ -32,6 +32,14 @@
 namespace {
 // Command prefix for injected JavaScript.
 const std::string kCommandPrefix = "paymentRequest";
+
+// Time interval between attempts to unblock the webview's JS event queue.
+const NSTimeInterval kNoopInterval = 0.1;
+
+// Time interval before closing the UI if the page has not yet called
+// PaymentResponse.complete().
+const NSTimeInterval kTimeoutInterval = 60.0;
+
 }  // namespace
 
 @interface PaymentRequestManager ()<PaymentRequestCoordinatorDelegate,
@@ -65,6 +73,13 @@ const std::string kCommandPrefix = "paymentRequest";
 
   // Coordinator used to create and present the PaymentRequest view controller.
   base::scoped_nsobject<PaymentRequestCoordinator> _paymentRequestCoordinator;
+
+  // Timer used to periodically unblock the webview's JS event queue.
+  base::scoped_nsobject<NSTimer> _unblockEventQueueTimer;
+
+  // Timer used to close the UI if the page does not call
+  // PaymentResponse.complete() in a timely fashion.
+  base::scoped_nsobject<NSTimer> _paymentResponseTimeoutTimer;
 }
 
 // Synchronous method executed by -asynchronouslyEnablePaymentRequest:
@@ -282,9 +297,11 @@ const std::string kCommandPrefix = "paymentRequest";
   // TODO(crbug.com/602666): Check that there *is* a pending response here.
   // TODO(crbug.com/602666): Indicate success or failure in the UI.
 
+  [_unblockEventQueueTimer invalidate];
+  [_paymentResponseTimeoutTimer invalidate];
+
   [self dismissUI];
 
-  // TODO(crbug.com/602666): Reject the promise on failure.
   [_paymentRequestJsManager resolveResponsePromise:nil];
 
   return YES;
@@ -322,6 +339,26 @@ const std::string kCommandPrefix = "paymentRequest";
     (web::PaymentResponse)paymentResponse {
   [_paymentRequestJsManager resolveRequestPromise:paymentResponse
                                 completionHandler:nil];
+
+  // Establish a timer that periodically prompts the JS manager to execute a
+  // noop. This works around an issue where the JS event queue is blocked while
+  // presenting the Payment Request UI.
+  _unblockEventQueueTimer.reset(
+      [[NSTimer scheduledTimerWithTimeInterval:kNoopInterval
+                                        target:_paymentRequestJsManager
+                                      selector:@selector(executeNoop)
+                                      userInfo:nil
+                                       repeats:YES] retain]);

[Moe, 2017/01/16 21:52:58]

is executeNoop what fixes the landscape issue? Why is it only necessary after
the payment is completed? 

[Justin Donnelly, 2017/01/18 19:36:21]

Correct, this fixes the landscape issue. Switching orientation is one thing that
causes the event queue to wake up, but it turns out that any messaging to the
web view also solves the issue.

It's necessary when the user hits the Pay button, which is what this method is
handling. At that point, the PR.show() promise is resolved and that's when the
page may do some asynchronous work (xhr or setTimeout simulating same).

+
+  // Per the spec, if the page does not call PaymentResponse.complete() within
+  // some timeout period, user agents may behave as if the complete() method was
+  // called with no arguments.
+  _paymentResponseTimeoutTimer.reset(
+      [[NSTimer scheduledTimerWithTimeInterval:kTimeoutInterval
+                                        target:self
+                                      selector:@selector(handleResponseComplete)
+                                      userInfo:nil
+                                       repeats:NO] retain]);
 }
 
 #pragma mark - PaymentRequestWebStateDelegate methods