Use a two-part data format version in IndexedDB metadata.

content/common/indexed_db/indexed_db.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // TODO: This will move to //third_party/WebKit when //content/child/indexed_db
 // is deleted but for now this will depend on //content/common types and so
 // so belongs here.
 
 module indexed_db.mojom;
 
@@ skipping 144 matching lines @@
   int64 id;
   array<int64> scope;
 };
 
 struct ObserverChanges {
   map<int32, array<int32>> observation_index_map;
   map<int32, ObserverTransaction> transaction_map;
   array<Observation> observations;
 };
 
+// Contains version data for the wire format used for encoding IndexedDB values.
+// A version tuple (a, b) is at least as new as (a', b')
+// iff a >= a' and b >= b'.
+struct DataFormatVersion {
+  uint32 v8_version;
+  uint32 blink_version;
+};
+
 // The Callbacks interface is used to return results for individual requests.
 // Some requests may return multiple results before completion, such as
 // UpgradeNeeded before SuccessDatabase.
 //
 // TODO(https://crbug.com/627484): Many of these could be replaced with
 // replies associated with particular messages.
 interface Callbacks {
   Error(int32 code, mojo.common.mojom.String16 message);
 
   // Factory::GetDatabaseNames
@@ skipping 142 matching lines @@
   RenameIndex(int64 transaction_id,
               int64 object_store_id,
               int64 index_id,
               mojo.common.mojom.String16 new_name);
   Abort(int64 transaction_id);
   Commit(int64 transaction_id);
   AckReceivedBlobs(array<string> uuids);
 };
 
 interface Factory {
+  // The backing store for a given origin should only be opened by clients
+  // configured with the same supported data version. It is assumed that this
+  // version is fixed at runtime.

[dcheng, 2017/04/04 19:59:21]

It kind of feels like this could even bound at compile time--it doesn't seem
like either the v8 or blink version should be changing past that point?

+  Configure(DataFormatVersion supported_data_format_version);
+
   GetDatabaseNames(associated Callbacks callbacks, url.mojom.Origin origin);
   Open(associated Callbacks callbacks,
        associated DatabaseCallbacks database_callbacks, url.mojom.Origin origin,
        mojo.common.mojom.String16 name, int64 version, int64 transaction_id);
   DeleteDatabase(associated Callbacks callbacks, url.mojom.Origin origin,
                  mojo.common.mojom.String16 name, bool force_close);
 };