[Payment] changePaymentMethod should work when details is empty or null

According to PH w3 spec the "details" input of the changePaymentMethod
should be optional[1]. Even though payment_request_event.idl honors the
spec[2],the blink implementation and the mojom file treat "details"
as a mandatory field. This cl fixes the issue.


Test coverage:
I reproduced the bug by removing the "details" field from
changePaymentMethod call[3]; The following two tests pass only after
applying the fix in this cl and fail without it:
MerchantResponse/PaymentHandlerChangePaymentMethodTest.Test/0
MerchantResponse/PaymentHandlerChangePaymentMethodTest.Test/1

[1]https://w3c.github.io/payment-handler/#the-paymentrequestevent
[2]https://cs.chromium.org/chromium/src/third_party/blink/renderer/modules/payments/payment_request_event.idl?l=23
[3]https://chromium-review.googlesource.com/c/chromium/src/+/2254084/2/components/test/data/payments/change_payment_method_app.js#32

Bug: 1083193
Change-Id: Ia479401d021be2d110a7a7ad4fe652d2eae4d88c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254084
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Liquan (Max) Gu <maxlg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781380}

components/payments/content/payment_handler_host.cc

@@ -124,7 +124,7 @@ void PaymentHandlerHost::UpdateWith(
         data.emplace(prefix + " Method Name",
                      modifier->method_data->method_name);
         data.emplace(prefix + " Method Data",
-                     modifier->method_data->stringified_data);
+                     modifier->method_data->stringified_data.value_or("{}"));
         if (!modifier->total)
           continue;
         data.emplace(prefix + " Total Currency", modifier->total->currency);
@@ -187,8 +187,10 @@ void PaymentHandlerHost::ChangePaymentMethod(
     return;
   }
 
+  const std::string stringified_data =
+      method_data->stringified_data.value_or("{}");
   if (!delegate_->ChangePaymentMethod(method_data->method_name,
-                                      method_data->stringified_data)) {
+                                      stringified_data)) {
     RunCallbackWithError(errors::kInvalidState, std::move(callback));
     return;
   }
@@ -202,7 +204,7 @@ void PaymentHandlerHost::ChangePaymentMethod(
         "Change payment method",
         /*instance_id=*/payment_request_id_for_logs_,
         {{"Method Name", method_data->method_name},
-         {"Method Data", method_data->stringified_data}});
+         {"Method Data", stringified_data}});
   }
 
   change_payment_request_details_callback_ = std::move(callback);

components/test/data/payments/change_payment_method_app.js

@@ -16,7 +16,7 @@ self.addEventListener('canmakepayment', (event) => {
  * @param {PaymentRequestEvent} event - The event to respond.
  * @return {PamentDetailsUpdate} - The update to the payment details.
  */
-async function responder(event) {
+async function responder(event) { // eslint-disable-line no-unused-vars
   const methodName = event.methodData[0].supportedMethods;
   if (!event.changePaymentMethod) {
     return {
@@ -29,9 +29,7 @@ async function responder(event) {
   }
   let changePaymentMethodReturned;
   try {
-    const response = await event.changePaymentMethod(methodName, {
-      country: 'US',
-    });
+    const response = await event.changePaymentMethod(methodName);
     changePaymentMethodReturned = response;
   } catch (error) {
     changePaymentMethodReturned = error.message;

third_party/blink/public/mojom/payments/payment_handler_host.mojom

@@ -20,7 +20,7 @@ struct PaymentHandlerMethodData {
   // object, so more specific types cannot be used. A simple example:
   //
   // {"supportedNetworks": ["visa"]}
-  string stringified_data;
+  string? stringified_data;
 };
 
 struct PaymentHandlerModifier {

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

@@ -185,14 +185,6 @@ ScriptPromise PaymentRequestEvent::openWindow(ScriptState* script_state,
   return promise;
 }
 
-ScriptPromise PaymentRequestEvent::changePaymentMethod(
-    ScriptState* script_state,
-    const String& method_name,
-    ExceptionState& exception_state) {
-  return changePaymentMethod(script_state, method_name, ScriptValue(),
-                             exception_state);
-}
-
 ScriptPromise PaymentRequestEvent::changePaymentMethod(
     ScriptState* script_state,
     const String& method_name,
@@ -213,7 +205,8 @@ ScriptPromise PaymentRequestEvent::changePaymentMethod(
   }
 
   auto method_data = payments::mojom::blink::PaymentHandlerMethodData::New();
-  if (!method_details.IsEmpty()) {
+  if (!method_details.IsNull()) {
+    DCHECK(!method_details.IsEmpty());
     PaymentsValidators::ValidateAndStringifyObject(
         script_state->GetIsolate(), "Method details", method_details,
         method_data->stringified_data, exception_state);