[AF][Nickname] Add proto change for nickname

Add new string nickname to WalletMaskedCreditCard, also update
corresponding proto_visitor. We will update other copies of
this proto in other places as a follow up.

Please refer to design doc for more info: go/nicknames-autofill-dd

Bug: 1059087
Change-Id: I1a1f666e96049e9dec40a53ec4085bbcb4b1f3c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2090770
Commit-Queue: Sujie Zhu <sujiezhu@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Jared Saul <jsaul@google.com>
Cr-Commit-Position: refs/heads/master@{#747794}

components/sync/protocol/autofill_specifics.proto

@@ -158,6 +158,9 @@ message WalletMaskedCreditCard {
   // Use WalletCreditCardCloudTokenData instead. This field will be set if
   // a cloud token is available for the instrument.
   optional CloudTokenData cloud_token_data = 11;
+
+  // The card's nickname, if it exists.
+  optional string nickname = 12;
 }
 
 // Different than an AutofillProfile because this represents some known address

components/sync/protocol/proto_visitors.h

@@ -1072,6 +1072,7 @@ VISIT_PROTO_FIELDS(const sync_pb::WalletMaskedCreditCard& proto) {
   VISIT(exp_year);
   VISIT(billing_address_id);
   VISIT(bank_name);
+  VISIT(nickname);
 }
 
 VISIT_PROTO_FIELDS(const sync_pb::WalletMetadataSpecifics& proto) {