[Play Billing] Add versioning to digital_goods.mojom.

This CL adds versioning to the digital_godos.mojom file in the blink.
This is required because some structs and enums are depended on by a
mojom file that is in components/arc/mojom, which is used by the browser
to talk to ARC++. There is a chance that the mojom files in ARC++ and
Chrome will be out of sync.

Bug: 1137688
Change-Id: I5716088509145cbe8c68fc9dfa879f44e1ff85cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2503753Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Glen Robertson <glenrob@chromium.org>
Commit-Queue: Jeevan Shikaram <jshikaram@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824372}

third_party/blink/public/mojom/digital_goods/digital_goods.mojom

@@ -2,6 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// This file is versioned solely for the convenience of sharing struct and enum
+// definitions with with an external repository. Do not add any
+// browser <-> renderer specific definitions or any browser <-> external
+// repository specific definitions in this file.
+// Specifically interfaces defined here must not be versioned.
+
+// Next MinVersion: 1
+
 module payments.mojom;
 
 import "components/payments/mojom/payment_request_data.mojom";
@@ -41,6 +49,7 @@ interface DigitalGoodsFactory {
         pending_remote<DigitalGoods>? digital_goods);
 };
 
+[Extensible]
 enum BillingResponseCode {
   kOk,
   kError,
@@ -64,6 +73,7 @@ struct ItemDetails {
   string? introductory_price_period;
 };
 
+[Extensible]
 enum CreateDigitalGoodsResponseCode {
   kOk,
   kError,
@@ -81,6 +91,7 @@ struct PurchaseDetails {
   bool will_auto_renew;
 };
 
+[Extensible]
 enum PurchaseState {
   kUnknown,
   kPurchased,