[Payment Request] Don't crash on multiple CanMakePayment responses.

Bug: 891371
Change-Id: Iea90f598eac5693b6797efa9ca91cabf7b097326
Reviewed-on: https://chromium-review.googlesource.com/c/1258023
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596020}

third_party/blink/renderer/modules/payments/payment_request.cc

@@ -1341,7 +1341,10 @@ void PaymentRequest::OnAbort(bool aborted_successfully) {
 }
 
 void PaymentRequest::OnCanMakePayment(CanMakePaymentQueryResult result) {
-  DCHECK(can_make_payment_resolver_);
+  // TODO(https://crbug.com/891371): Understand how the resolver could be null
+  // here and prevent it.
+  if (!can_make_payment_resolver_)
+    return;
 
   switch (result) {
     case CanMakePaymentQueryResult::WARNING_CAN_MAKE_PAYMENT: