PaymentHandler: Implement PaymentInstruments.has().

components/payments/mojom/payment_app.mojom

Index: components/payments/mojom/payment_app.mojom
diff --git a/components/payments/mojom/payment_app.mojom b/components/payments/mojom/payment_app.mojom
index ccda4c7df095eb0562b9794848ccf7a59b457097..e73083717d358611af8eeb4d1ae30e03116d6536 100644
--- a/components/payments/mojom/payment_app.mojom
+++ b/components/payments/mojom/payment_app.mojom
@@ -52,6 +52,8 @@ interface PaymentManager {
       => (PaymentHandlerStatus status);
   SetPaymentInstrument(string instrument_key, PaymentInstrument instrument)
       => (PaymentHandlerStatus status);
+  HasPaymentInstrument(string instrument_key)

[Tom Sepez, 2017/04/26 16:20:15]

Isn't this a subset of the functionality of Get()?  Do you need to do this
rather than just a get discarding the |instrument| result?

[zino, 2017/04/26 17:35:21]

The function is defined in the spec. (It's a map-like interface)
Anyway, we will able to share the get() implementation and then provide
different functions in only blink side.

But I'm not sure what is advantage. If we use get() implementation, then we will
have to read and deserialize stored data unnecessarily whenever just calling
has() method.

+      => (PaymentHandlerStatus status);
   GetPaymentInstrument(string instrument_key)
       => (PaymentInstrument instrument, PaymentHandlerStatus status);
 };