Add billing address identifier to WalletMaskedCard.

BUG=602663

Review-Url: https://codereview.chromium.org/2058513002
Cr-Commit-Position: refs/heads/master@{#399278}

sync/protocol/autofill_specifics.proto

@@ -111,12 +111,14 @@ message WalletMaskedCreditCard {
 
   // Four-digit year (e.g. 2017).
   optional int32 exp_year = 7;
+
+  // The WalletPostalAddress.id of the billing address.
+  optional string billing_address_id = 8;
 }
 
 // Different than an AutofillProfile because this represents some known address
 // on the server that is pulled down rather than synced between Chromes.
 message WalletPostalAddress {
-  // DEPRECATED
   optional string id = 1;
 
   optional string recipient_name = 12;

sync/protocol/proto_value_conversions.cc

@@ -697,12 +697,14 @@ std::unique_ptr<base::DictionaryValue> WalletMaskedCreditCardToValue(
   SET_STR(last_four);
   SET_INT32(exp_month);
   SET_INT32(exp_year);
+  SET_STR(billing_address_id);
   return value;
 }
 
 std::unique_ptr<base::DictionaryValue> WalletPostalAddressToValue(
     const sync_pb::WalletPostalAddress& proto) {
   std::unique_ptr<base::DictionaryValue> value(new base::DictionaryValue());
+  SET_STR(id);
   SET_STR(recipient_name);
   SET_STR(company_name);
   SET_STR_REP(street_address);