1. Add "optional Promise<PaymentDetailsUpdate> detailsPromise" as a parameter
of PaymentRequest.show() in PaymentRequest.webidl.
2. Let PaymentRequest inherit from PromiseNativeHandler, and implement the
ResolvedCallback() and RejectedCallback() to handle the PaymentDetailsUpdate
promise.
3. Update PaymentRequest.show() implementation. If PaymentDetailsUpdate Promise
is not nullptr, the show request would not be transferred to chrome process
immediately until the promise is resolved/rejected.
4. Update selectedShippingOption when requestShipping is true.
5. Change the PaymentMethod id validation sequence according to the spec.
