1. Create a new action response status PAYMENT_NOTSUPPORTED and get rid of
unnecessary method isAccpeted() from nsIPaymentActionResponse.idl.
2. Create canMakePayment() in PaymentRequestService and run it before
launching UI. If canMakePayment() returns false, send PAYMENT_NOTSUPPORTED
back to content process.
3. If chrome process returns PAYMENT_NOTSUPPORTED when calling showPayment(),
throw NotSupportedError DOMException to merchant side.
Getting the top level document's principal when constructing PaymentRequest,
then sending it to chrome process and saving it in nsIPaymentRequest.
Creating a new readonly attribute nsIPrincipal topLevelPrincipal in
nsIPaymentRequest for UI to query the top level document's principal
information.
Eden Chuang
Wes Kocher
Ryan VanderMeulen