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

content/common/indexed_db/indexed_db.mojom

Index: content/common/indexed_db/indexed_db.mojom
diff --git a/content/common/indexed_db/indexed_db.mojom b/content/common/indexed_db/indexed_db.mojom
index 16b8e9ad0be1985b546af3668e4bd631c817124b..2d8264958de319f6a8088e83cadbae1433df8123 100644
--- a/content/common/indexed_db/indexed_db.mojom
+++ b/content/common/indexed_db/indexed_db.mojom
@@ -162,6 +162,14 @@ struct ObserverChanges {
   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.
@@ -324,6 +332,11 @@ interface Database {
 };
 
 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,